Power and fans but no post, no nothing...sometimes

I'm troubleshooting a laptop. If I let it sit for a couple hours and turn it on, I get a post message, and it boots up just fine. However, if I turn the computer off then back on or reboot, it has power and the fans turn on, but I get no post message. I can't even turn on caps lock. It does poll the CDROM, however, as that makes a noise.

I opened it up, swapped the RAM around, and then it booted just fine. However, a day later, the problem presented itself once again. So, I reopened it and unplugged and replugged the harddrive, and it booted just fine. But, then the problem came back upon reboot.

FWIW, it has Vista installed...but clearly this is not a software problem.

Any ideas on what the problem is? Does this sound likely to be a harddrive problem?

From serverfault Chad Johnson

• Sounds more like a PSU issue to me.

  From Keiran Holloway