So I'm building a computer for a friend, and we just finished getting everything in and attempted to turn it on. When we hit the power button, fans came on, video card fan came on, CPU fan, everything turned on except the monitor. Then it shut off for a second, then turned right back on. It's doing this repeatedly, when we turn it on, it comes on for a second, turns off for a second, then turns back on, and either repeats the process over and over, or just stays running.

Sound like the motherboard to anyone else?

I tried resetting the CMOS and reseating the CPU heatsink/fan as well as reseating the RAM adn the videocard.

Here are the specs:

XFX 8800GTS
Intel E6600
Gigabyte P35-DS3P
2 Gigs Corsair XMS2

Motherboard?

EDIT: Out of sheer curiosity I reseated the video card again, and now we have a horrendous post beep that's just one long beep and doesn't stop. To edit the edit, i'm a retard and forgot to hook the power back to the video card, plugged it in and the beeping stopped. Still no go though.

Well it sounds like a bad video card. But it could be insufficent power.
What kind of Power Supply do you have? (Manufacturer, Model, Watts)

My first guess would be motherboard.

The video card and memory are easy to check in another system.

I have to agree with slaymate on this one......

My two cents are going on the power supply. A generic one /multi-rail psu may not be putting out enough juice to handle that video card and can cause all kinds of stability issues. I definately recommend posting your power supply specs as stated above. If possible i would use a multimeter and see what kind of juice is coming out of that power supply. You can pickup an inexpensive one for less than $20 at a menards or home depot.