Hi and welcome to FpcH
I assume that the system does not boot up?I'm pretty sure i've blew the motherboard
Before you buy a new m/b why not check it out ( as best we can ) first?
Do you get any POST beeps when you try to boot up?
( assuming that you got one beep before )
Does the keyboard light up and are there any LEDs lit on the m/b ?
If you are NOT getting POST beeps ( and you did before ) ......
Switch off at the wall - leave the plug in to maintain the earth ( ground ) connection.
Then I would strip everything off the m/b ( RAM / Video Card etc ). Disconnect all external devices.
Disconnect the power to the hard drive and DVD Drive.
Disconnect the drives' data cable at the m/b end.
Leave only the 20(4) way connection from the PSU
You should get POST beeps if you have an internal speaker.
If you don't then it is a problem with the PSU or m/board.
If you DO need to replace the m/b then you will invariably need to re-install the OS on your hard drive.
(unless you have XP then you can do a repair install)
You may want to get at the data on the hard drive to re-claim it.
This is easily done.