Random boot problems

[guignol]

Hey all,
I have a problem with my desktop and I can't seem to pinpoint the reason.
No luck on different troubleshooting guides or flow charts...

It used to have two modes:
- Dead (no POST single beep, screen & PC lights on)
- Alive (working fine)
Which means that I had to start my PC, unplug, re-plug, re-start, etc. between a few and several dozen times before it really started, at which point it worked perfectly fine, for a few days if needed.
Usually, the colder it was in the room (that was a hard winter here), the more problems there were.

Now, things have gotten worse. The "Dead" mode is still here, but if POST single beep is heard, it can afterwards stop & freeze at any point during the boot process, including:
- while calculating CMOS checksum
- while writing the summary (sometimes writing suddenly FFFF and stopping)
- during the black screen with a white bar when loading MS 2000
- during the MS 2000 color page (with the blue bar)
- while loading personal informations
- when everything seems loaded and working fine (freezing)
It can also freeze after working fine for some time.
And it also sometimes finally works perfectly, like right now, and I can do whatever I want. It takes several minutes, but for now I've always managed to finally start the PC correctly, nonetheless it's getting worse by the day.

After problems have started, and sometimes for unrelated reasons, I have changed CMOS battery, added some RAM, I also checked condensators, and they look fine, although one are two were a bit dusty. According to the EVEREST Software, temperatures seem coorect (CPU 60°C, MB 40 °C)

Basically, I'm lost.
Does anyone have any idea about the cause of this ?

Excessively thankful for any input,
Guillaume.

[ski]

60C and 40C are a little toasty for CPU and system temperatures respectively, especially if the system is running in a cool environment, and when it's either at idle or performing non-intensive applications without multi-tasking(e-mail, Internet browsing, simple programs, etc.), and that may be why it's freezing once it's up and running.
Make sure that all fans are running(incl. those in the power supply), all vents are unobstructed, clean out any dust built up on all fans/heatsinks and inside the case, and make sure that all heatsinks are fully secured. You may also want to remove the CPU's heatsink, clean off the thermal compound from the CPU's die and heatsink with 91%(or higher) alcohol and a soft cloth, and apply Arctic Silver thermal paste.
If that does not help, then remove the computer's cover, and run an external fan. If this works, then either additional or more powerful case fans are needed. Lower front blowing in and upper rear(or top) blowing out are the recommended locations and air direction orientations.

WRT the startup problem, it's possible that the power supply may be the cause.
Swap it out with a different known working unit of similar capacity and identical design.

[Sylvander]

1. Your PC was never "dead" [you had LED's glowing].
So it was probably NO POST when it did that.

Is the heatsink fan noisy?
I once had an intermittent failure to POST that was caused by a fan beginning to go bad and probably shorting the PSU.
Sometime it would POST without any problem, other times not.
When I replaced it the problem went and hasn't returned since.
If its not a faulty fan, what about the fitting of the heatsink, is it ok?
Could it be an overheating CPU?