Video sporadically won't function

I recently pulled my old computer (2006 build, slight upgrades in 07 and 08) out from storage (sat there two years) and now it's having trouble working with my display properly.

It originally worked for about a night and then when I woke up the video wasn't working. A few days later I got it working again using a DVI to VGA adapter, but it didn't get very far before not working anymore (windows was loading but not sure if it went to desktop).

The computer has an Athlon 64 X2 4600+ on this mobo running Win7 32-bit. I can't connect to the mobo so I try using the two DVI ports on my 8800 GT. I'm trying to connect to a KDS monitor (can't find model), which I know works fine as I'm using it right now, connected to a laptop over VGA. I unplugged the VGA cable when I tried to use the DVI.

I'm kind of assuming it's my video card but would prefer to be able to be sure if possible without buying a new one. The first time I got it to work was using a 10 ft DVI cable, but it took a lot of tries (use both ports, reboot multiple times) and not really sure what changed when it did work. As I said, it worked fine for a few hours but then went out overnight. A few days later I got a DVI to VGA connector and it seemed to work pretty quickly but then only for a minute, before fully booting into desktop. AFAIK everything else in computer works fine.

I really appreciate any help you guys are able to provide, thanks.

Btw, if my video card doesn't work I am thinking about getting a new cpu/mobo/ram (i3/h61) but not sure if I should also replace my PSU, a 6 year old Antec TruePowerII-550 or how I would connect my new mobo to my IDE optical drives and IDE hard disk drives. I assume I could go without a video card for awhile and use mobo's video output ?