Need help determining if i need to change my motherboard

[iamlookingforthebathroom]

Hello. I have this problem with my girlfriend's computer that would occasionally boot for like 30 seconds and then the image would go off. For most of the part it would power up and i can hear a repeating sound made by the DVD-ROM while its LED flashes but there's no image on the screen( no boot ). What i have tried is :
- Switching over four GPUs ( AGP 8x ) to see if it's a video card problem.
- Switching RAMs with other ones that work.
- Removing every part except the processor ( AMD Athlon 64 3200Mhz ) and then placing them back one by one.
- Removing the motherboard's battery which actually led to the system powering up and booting into windows( XP SP3 ) for like 15 seconds after which i got a blank screen.
- Removing the PCI network card from the system.

The mouse and keyboard are receiving power , also the CPU fan is spinning, the DVD-ROM gets powered up and the HDD shouldn't be a problem when troubleshooting since with having it removed i still can't get even a BIOS welcoming screen. It kind of stays in a state of trying to boot so i suspect that the motherboard is not working properly. I am asking for a bit of advice before i wrap it up and send it back ( i bought it last year in November so it's still in warranty ). Thanks a lot.

 

[Cyber023]

It sounds like the motherboard can't initiailze the CPU or CPU FAN (check if cable if connected in the correct port on the mobo) and the pc shutsdown as a security musure.

 

[iamlookingforthebathroom]

The CPU fan gets powered. Even the GPU's fan is spinning. Everything seems to power up but i get no image. I don't have a speaker installed on the case so i can't follow the beep error codes. The PSU is also new though this seems like a PSU problem. I have assembled a new computer lately with brand new parts and when I forgot to plug in an 8 pin chord into the motherboard the symptoms were pretty much the same as those i get from troubleshooting this computer, meaning that all the parts are being powered but the boot up sequence doesn't take place.