My current problem is that the cpu fans run at 100% and my computer won't boot. There's some history to this problem, and I don't know whether or not it's relevant, so I'll write it all down.
A few weeks ago, my computer started randomly rebooting itself. Initially I ignored the problem, but the reboots became so frequent that I started to investigate. I tried booting from a CD (didn't use the hard drive at all), and the reboots continued.
From some research on the web and discussions with IT, it sounded like the problem was probably the power supply. I opened up the computer to look around inside, and at some point when I tried to reboot with the cover open, the fan went nuts (louder than I've ever heard a computer fan run). I shut down, I think by pulling the power cord, closed the computer, maybe moved it around a bit, and rebooted, and the loud fan problem went away. Okay, so at this point I still assumed that the power supply was my main problem and the loud fan was a transient event.
I ordered a new supply, and finally got it installed today. Installation was pretty simple -- not a lot to mess up. When I tried to boot the machine, the fans went completely nuts, blowing at 100% continuously until I shut the computer down. Also, the computer does not appear to be booting at all -- I get nothing on the monitor. But I've occasionally had problems getting this computer and monitor working together (monitor has two different inputs, bad UI, video card has two outputs). However, it doesn't appear that the computer boots at all, so the other posts I've read about fans running in overdrive don't help.
I'm at a loss for what to try next. Any ideas?
There are 3 elements to fan control. The thermal sensor inside the CPU, which you can disregard since this happens cold. The fan and its connections--if the control signal does not reach the fan it defaults to full speed. The chipset, which at startup loads a control constant from BIOS, but of course the chipset must be running to do this and it sounds like yours isn't.
Your advisors were on the right track about power, and the power supply is cheaper to try than the motherboard. But half the power regulation is on the motherboard and it looks like that's where the problem is. At this time, the power light should be yellow and the diagnostic lights off. If you have those conditions, motherboard is most likely. Just to be sure it's not a cheaper accessory, unplug all plugin cards and USB and if the condition does not change you're back to motherboard.