|Make sure the case power button, that presses on the actual power switch, is not stuck inwards such that the switch is always pressed. The same applies to the Reset button if your case has one. |
It's extremely unlikely there is anything wrong with the installation of the cpu heat sink, unless you or someone else has been messing with it. It must be clamped to the mboard. If it isn't loose, there's probably nothing wrong with that.
Make sure the cpu fan spins at a reasonable speed when the computer is running.
If the cpu fan is spinning slower than it should, or if it makes rumbling or screeching noises, most likely to be noticed when the computer is first started up after having a chance to cool to room temp and has sat there for hours, the sleeve bearing(s) on the fan are in bad shape and you must replace the fan as soon as you can.
If the CPU fan and heatsink have too much dust and lint on them, clean them off, but DO NOT use a vacuum cleaner to do that.
A common thing that can happen with ram, even ram that worked fine previously, is the ram has, or has developed, a poor connection in it's slot(s).
In that case, your mboard may not boot.
See response 2 in this - try cleaning the contacts on the ram modules, and making sure the modules are properly seated:
For a laptop, or netbook, you must remove both its main battery and AC adapter before you do that.
For a brand name computer, see the Owner's or User's manual if you need to - how to remove or replace the ram is usually in that - it may already be in your installed programs. If you can't get into Windows, it may be on a disk that came with the computer, or you can go online and look at it or download it - it's in the downloads for your specific model.
For a generic desktop computer, see the mboard manual if you need to - how to remove or replace the ram is usually in that.
Some mboards develop this problem - electrolytic capacitors were installed on them that were not properly made, and they fail eventually - the mboard manufacturer didn't know they were improperly made at the time the mboard was made.
Open up your case and examine the mboard to see if you have bad capacitors, and/or other findable signs of mboard damage .
This was the original bad capacitor problem - has some example pictures.
History of why the exploding capacitors and which mboard makers were affected:
What to look for, mboard symptoms, example pictures:
Home page that site
- what the problem is caused by
- he says there are STILL bad capacitors on more recent mboards.
Pictures of blown capacitors, other components, power supplies, Athlon cpu's, etc.: