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Help with Dell optiplex Desk Top

adeplus2

FPCH Member
Joined
Feb 15, 2014
Messages
9
PC Experience
Beginner
#1
Hi all,
I recently bought a Dell Optiplex 755, recently a fault has occured with it, which no video is shown on the monitor. I have verified the monitor and the connection cable is not at fault, as I have tested with other devices and they work with it.
I have reset everything inside the box but again nothing is appearing on the screen, the fan is working and a a light is showing on the motherboard so power is getting through.
If anyone is able to help, please do so, I have no idea on the problem and wish to spend as little as possible on repairs.
 

KenB

Administrator
Joined
Oct 19, 2008
Messages
9,245
Location
Wirral UK
#2
Hi and welcome to FpcH

You have recently bought this machine ............ is it new or used ?

If it is new you should be able to take it back for repair / replacement.

The fact that fans run and LEDs are lit is no indication that the Power Supply Unit is OK.
It can be faulty and still provide enough power to run fans etc.

Does the machine actually try to boot up ?
Do you get any Beeps ?
If so - what sequence are they ........ one long two short for instance.

If this is new you do not want to start removing / changing hardware as it could invalidate any warranty that you have.
 

adeplus2

FPCH Member
Joined
Feb 15, 2014
Messages
9
PC Experience
Beginner
#3
Hi KenB
This is secondhand computer that was working well until this point.
The machine turns on and seems to power up fine, just nothing on the screen.
It did beep several times it quick order, but does not now, I have just powered it up and there are no beeps now,
 

KenB

Administrator
Joined
Oct 19, 2008
Messages
9,245
Location
Wirral UK
#4
Second hand ...... does it have any warranty ?

I wrote a tutorial re: "No POST Beeps"
click here

If , when you have stripped the m/board down you can get POST beeps - this is good news.
If not then we are looking at PSU or m/board.
 

adeplus2

FPCH Member
Joined
Feb 15, 2014
Messages
9
PC Experience
Beginner
#5
Hi KenB,
I followed the tutorial to my best, stripping the computer to what your specifics said, and no beep was heard. All cards and wires were disconnected from the motherboard (that I can see and reach) and the disc drive and hard drive were fully disconnected from the motherboard. My end result was no beep heard, if being either the PSU or Motherboard is at fault, are any costs needed to make sure the computer is fully functional? Or can I simply twist something and a spark of life will be sent through the machine?
 
Last edited:

KenB

Administrator
Joined
Oct 19, 2008
Messages
9,245
Location
Wirral UK
#6
If you know the system used to Beep and it isn't now - this isn't good.

Are you sure you pulled the RAM / Video Card / etc off the m/board and that you had the 20(4) way power connection from the PSU connected.
If this is correct then I suggest that you take a look at the PSU next.

This is the cheapest option.

I wrote a tutorial on how to test the PSU - click here

You can buy a tester similar to this one ..click here

The best way to is to swap it for another if you can
 

adeplus2

FPCH Member
Joined
Feb 15, 2014
Messages
9
PC Experience
Beginner
#7
Hi KenB

Update so far, changed motherboard and PSU and the same problem persists.

The machine switches on seems to be running fine, there are no beeps, but the monitor remains blank with the orange instead of green light indicating nothing is coming through. We have tested the monitor, it is fine and swapped the monitor cable just in case.

The machine simply won't boot up at all with either old or new MB or PSU, any other ideas appreciated?

-Edit-

Would it help if I took a picture of the inside and posted it on this thread?
 
Last edited:

Plastic Nev

Deceased - sadly missed
Joined
Oct 19, 2008
Messages
5,442
Location
Lancashire
#8
Hi, is the new motherboard exactly the same make and model as the original?
If not, you may not get it to boot anyway as windows is fussy about that.

However, with the new motherboard and PSU, is there a separate video graphics card or is the graphics integrated with the motherboard?
If a card, it may be that at fault.

The other possibility if you used the original CPU, that could be faulty though very rare.

However my bet now is the hard drive faulty.

To find that out is to remove it, use a USB adapter, or enclosure, or if one available to borrow, a hard drive to USB docking station and connect it to a working computer, then see if the working computer recognises it and that you can access the data on it.

Nev.
 

KenB

Administrator
Joined
Oct 19, 2008
Messages
9,245
Location
Wirral UK
#9
Hi
A pic of the inside would not really help us identify your problem.

Before you try what Nev has suggested:

Take the side panel off - then switch on and try to boot up.

1. Are all of the fans spinning - especially the CPU fan ?
2. Can you hear the hard drive spinning up

3. Take the RAM out and switch on - do you get any beeps now?
 

adeplus2

FPCH Member
Joined
Feb 15, 2014
Messages
9
PC Experience
Beginner
#10
Hi
A pic of the inside would not really help us identify your problem.

Before you try what Nev has suggested:

Take the side panel off - then switch on and try to boot up.

1. Are all of the fans spinning - especially the CPU fan ?
2. Can you hear the hard drive spinning up

3. Take the RAM out and switch on - do you get any beeps now?
I have tested the computer with your advice, the fans do spin (there is only one), I can confirm the hard drive does spin and there are no beeps when the RAM is taken out.
Does that mean the RAM is at fault?
 

adeplus2

FPCH Member
Joined
Feb 15, 2014
Messages
9
PC Experience
Beginner
#11
Hi, is the new motherboard exactly the same make and model as the original?
If not, you may not get it to boot anyway as windows is fussy about that.

However, with the new motherboard and PSU, is there a separate video graphics card or is the graphics integrated with the motherboard?
If a card, it may be that at fault.

The other possibility if you used the original CPU, that could be faulty though very rare.

However my bet now is the hard drive faulty.

To find that out is to remove it, use a USB adapter, or enclosure, or if one available to borrow, a hard drive to USB docking station and connect it to a working computer, then see if the working computer recognises it and that you can access the data on it.

Nev.
The motherboard is some what the same, the wire slots for the hard drive have been changed, but it is the same motherboard.
There is no graphics card I could find, it is intergrated from what I can tell. However I did try to install one, as there is a slot for it, but failed as there wasn't enough space for it.
I believe the hard drive does work, as it spins when its turned on.
 

KenB

Administrator
Joined
Oct 19, 2008
Messages
9,245
Location
Wirral UK
#12
no beeps when the RAM is taken out.
Does that mean the RAM is at fault?
No - not at all.
With the RAM removed you should get POST beeps.

Take a look here - click here

If you have tried all of this then you need to check out the Hard Drive as Nev suggests.

I am a little confused as you say that you have changed the PSU and m/board - you should get POST Beeps if you did before.
 

adeplus2

FPCH Member
Joined
Feb 15, 2014
Messages
9
PC Experience
Beginner
#15

No - not at all.
With the RAM removed you should get POST beeps.

Take a look here - click here

If you have tried all of this then you need to check out the Hard Drive as Nev suggests.

I am a little confused as you say that you have changed the PSU and m/board - you should get POST Beeps if you did before.


I tried your advice again, the result was the same. No POST beeps but with the new motherboard and power supply units. I don't know what else to do, could it be wire faults? Or just a faulty computer?
 

KenB

Administrator
Joined
Oct 19, 2008
Messages
9,245
Location
Wirral UK
#18
It could be that one of them is faulty too.

If your system has an internal speaker ( working ) then with the board stripped sight down to just the 20(4) way connection from the PSU - it should give you POST beeps.
If it doesn't - as already stated - then this implies m/board or PSU.

1. Are you sure that you used the stand-offs from the old m/board when you fitted the new one?

2. Strip the board right down - leave the 20(4) way cable connected.
Unscrew the m/board and sit it on some card or newspaper to insulate it from the case.
Switch on.
If you get POST beeps now then there was a short between the m/board and the case.
( Look at the stand-offs )

3. If the above doesn't help then check out the PSU - click here
You could always ask a local tech to test it for you - ask how much this would cost.

I really think that your problem lies with either the PSU or the m/board as it cannot be anything else.