I have a three+ year old Sony VGN-S260 and one day out of the blue it did not start. Some times it will start just fine, but others it will not. The symptoms are odd because the led lights that display battery, wifi, and hard drive are lighting up as though it is on. Yet, the hard drive is not spinning. I attempted to run hardware tests using a bootable cd, but the cd begins spinning after a little while only to stop again. I thought it might be the ram, but I am having a hard time finding new ram for it because it is micro dimm. Any suggestions?

My Compaq Presario model 2500 won't turn on atall. I tried to boot after removing battery, still it won't turn on.

How can I pinpoint the problem in hardware?

Here are the basic troubleshooting techniques I use to find a "mysterious" problem such as yours.

1. Remove battery and set it aside - try to POST
2. Remove HDD and set it aside - try to POST
3. Remove CDROM and set it aside - try to POST
4. Remove RAM and set it aside - try to POST (PCs can't POST without RAM silly man, duh, listen for a beep from your PC speaker. 99% of motherboards I've worked on give some sort of error beep when no RAM is installed.

Basically what you are doing is isolating all periferals until you find out if one of them is causing the no boot issue. Once you are down to nothing left, you can be sure it's a mobo or proc issue.