Bad mother board?

So I have two towers that I want to combine into one. well basically I want to put one hd into the other tower.

tower one: its old as hell but has been a flawless pc of mine for 4 years, it was my dads before that. I usually left it on always, just restarted it once a week or so. one day i restarted it and it never turned back on. I was able to plug the hd into my gf’s tower on the second port of the ribbon cable and it picked it up and I could get docs off of it.

tower two: a newer dell tower with lots of usb ports on the front and a multi card reader spot on the front as well. if you plug that in the power supply fan goes and maybe the mother board fan (i forget) and lights on the key board light up but the monitor does nothing. if you unplug the monitor from the video cord the monitor says it is looking for a signal, but it doesnt show anything when plugged in. this has an ati video card along with the ‘stock’ one.

the power supply for tower one works as I installed it on the second tower and the supply fan turned on. I believe the second tower is booting but nothing appears on the screen when hooked up to either monitor output. the first tower nothing happens. no beeps from either hd.

how do I diagnose the mother board further? what could be wrong with the frist tower that would cause it not to turn back on?

the first tower has always been virus free ever since I have owned it, the second one I have never seen run, i think it was my dads gf’s computer and prob has lots of viruses on it.

both power supplies are good and atleast one hd is good. I was going to swap hd’s but they arent even remotely close.

thanks

Bad PCI slot? have you tried different video cards in the Dell? is everything connected on the motherboard that should be?

I dont have another video card to swap. I can take out the ATI and just run the stock one I think.

With the older computer it just quit out of the blue. If iI hadnt restarted it I’m sure it would still be running.

the only thing I have unplugged from either mother board is the power supply and hd ribbon cables.