black screen need some help a little

here is my problem .
you know that i build 2 new pc .
on one of my new pc the power supply burn so i took the power supply from my old pc .
now yesterday i receive the new power supply for my old pc .i put it in all fine but no screen .black .
now all the fans are working .motherboard light is green .pcu is working.the hard drive is working .i did pull the ram out .put them back in .well i did try every thing .
well all is working but black screen .
now it is not my monitor because it is working fine on my 2 other pc .
i do not have a video card on my old pc .
so do you thing i should buy one .

now it is a ddr2 so i was thing of getting this video card .

ASUS GeForce 8400GS 589MHZ 512MB 677MHZ DDR2 Silent Low Profile DVI HDMI PCI-E Video Card

As long as you have selected the correct slot, pci, AGP, PCI-E it should do just fine.

Curious as every video card I have had go bad, I could not even boot the computer.

If this is the PC that the original PSU burned out on, then it may have taken out other components with it. Cheap power supplies have a tendency to do that, and you will get the symptoms that you describe. TBH, it sounds like motherboard failure to me :(

thank train
here is my old pc mother board info .
this is a 32bits ddr2
lga 775 -1066 or 800 mhz.
ram 667 or 533 .
on board video -gma-3000 .
now it take -pci expressx16 .
so is this video card do the job on that board .

MSI N8400GS-MD256H/TC GeForce 8400 GS 512MB Turbocache (256M) 64-bit PCI Express 2.0 x16 HDCP Ready Video Card

if you need all the info about the intel board .
i could copy the info and send it to you .
so i thing for 29.99 for the video card mentionned above be a good fix .what do you thing

How do you know that the problem lies with the graphics card?

i just don't know what happen .this computer was working fine 3 weeks ago when i took the power supply out of if .
now with the new one i cant not get the screen to come on .
do onboard video just blow like that .
because there is nothing to hook up a power supply .all you have is the 4 pin and the 24 pin power to plug so or cant you screw up some thing .
that get me

guess what happen .my board was still perfect it me that pull the [clear rtc ]right out of the board .i did not know what it was till yesterday when i was reading the user guide of my new board .
it a little plastic tab 2 pin .
like i said before there is a lot of stuff that i don't know yet .
now i know what that little plastic tab is .lol .
so it cust me a new computer for nothing .
ha well it was getting old anyway .