I had this exact problem yesterday where the CPU fan came on like a jet engine and the PC didn't start and the monmitor was blank. I simply opened the case, blew out ALL the dust bunnies, in the case and on all the boards and heatsink, fans etc, reseated all the power supply cables/connectors, especially the main pcb fan and 20 pin connector on the main pcb. When I plugged it back in, everything was fine. Yay!
Just clean all the dust from the heatsinks and reseat all the connectors. I did not fool around with the cpu or thermal paste etc.
I had the same problem with my old Dell and a new desktop. I think it was the problem with Tuneup Utilities program. In my old Dell, I removed the battery from motherboard. It worked!
For my new desktop, I noticed the fans running were not CPU fans. They were the side and back fan. Actually, the CPU fan was off. It did not turn on when I tried to restart the system from sleep mode. I did the following:
1) unplug all cables
2) unplug CPU fan wire from the motherboard
3) plug CPU fan wire again
4) Turn it on and the side and back fans turn back to normal
Thank you KEVDMD (above) for your thoughtful consideration in writing your post.
I was installing new memory (in Gateway PC) and thought the computer was shut down when it was actually in hibernation mode. I shut down when I was done and couldn't boot back up. Fan's were running and power was on, but nothing else.
Based on a few Google searches and subsequent forum discussions I came to the conclusion that I needed to reset the motherboard/bios via the pull battery method.
UNTIL I read kevdmd's post above.
Instead, I decided to pull the power chord in the back and drain all juice to the motherboard. After, I booted up and heard 3 beeps. Now i'm getting somewhere! I shut down again and ...VOILA! I couldn't be happier to hear Vista's startup theme!