PC won't boot at all, power is on but nothing displays?

[Flyingmantis]

Ok, here's the dealio. My cousin's PC was working fine not 2 hours ago. He left it going as he went out and when he came back it wasn't working. The PC was still on but nothing worked.
The case fan isn't spinning and the gpu fan is going at max speed. When the CD drive is plugged into the motherboard it does not open at all, but when unplugged it opens and closes fine.

What I tried:
I tried using a different PSU, same result.
I removed the GPU, same result.
I reseated the CPU and heatsink, same result.

Specs:
Intel Pentium 4 3.0ghz LGA 775
2GB DDR RAM
Nvidia 8500GT 512mb
The mobo is a "PTGD1 - LA" unsure as to what brand, possibly asus
400W Unbranded PSU
(Please be aware this was built out of scrap parts I had)

The PSU is fine and so are the HDD's and graphics card. There doesn't appear to be any capacitor leaking or bulging.

 

[dragonlord12832]

You said the case fan wasn't spinning. What about the CPU fan? Sounds like it got too hot. . .

 

[Flyingmantis]

CPU fan spins at a normal speed, COU wasn't the problem either, I think motherboard?

 

[walkingepidemic]

Hmmm. It may be unlikely, but have you tried resetting the CMOS by removing the battery and/or putting the jumper into the reset position?