NO FANS running on PCG GRT170

A buddy sent me his old(ish) VAIO to troubleshoot/have.

It's readily apparent upon powering up the machine that neither the CPU or system fan are turning at all. It actually boots up successfully (to Windows XP) and immediately turns off - I assume it's either sensing the cpu fan is not working, or hitting a cpu temperature alarm/threshold and auto-powering off. There are no errors in POST or Windows, you just catch a glimpse of the desktop before it completely bonks off. I haven't tried it more than 2 or 3 times for fear of damaging the CPU (duh); just enough times to confirm the problem whether running off of battery or plugged into AC power.

I popped it open and have tested both fans - they WORK when i ghetto rig each on a 9v battery (i know they are 5v fans). So now I'm down to figuring out how to troubleshoot it any further and whether the motherboard is done or if it's just some kind of wacky power issue? Since it actually boots to Windows that still gives me hope with the mobo. I don't know how I could test the fan headers since they're so tiny, but I guess that should be next... I think it's pretty clear though that they are not providing any juice.

Since it wasn't my computer previously I do not know if the cpu fan typically powers on before getting to Windows or not? though I assume it should.

Any experience/ideas?

Sony VAIO PCG GRT 170 (P4 2.8 ghz i believe)
probably just over 3 years old

 

UPDATE:
With the CPU fan churning full-bore on a standard 9v battery I've been able to boot and stay running indefinitely in Windows. So I think that should confirm that it was powering off only after hitting a critical CPU temp...

With it running I've tried getting my my multi-tester on each fan header, but haven't gotten anything. So either there's no 5v being supplied to the fans as I expected, or I'm not really getting good contact with my voltmeter...

I have no idea what to do next..... does anyone know where I can find a full diagram of the mobo/hardware?

 

Also having the same problem. Fans worked fine until I had to replace the dc jack. Was a straight forward repair, with a plug in harness. Computer starts up fine, everything seems to work as expected. But, no fans. Have not let it run for fear of heat damage. Does anyone know if sony uses grounding screws which would short out fans if not put back in. (Havn't put it completely back together)