I build computers as part of my business. Quite a few years ago, I was delivering a computer in January (so up to 20C difference in temp between indoors/outdoors). It was about a 45-minute drive, and when I set up the computer, it was totally unstable for about an hour after first switching it on (bear in mind, it worked flawlessly in my home). After that approximate-hour had passed, it was 100% stable (and has been ever since). I think it is pretty likely that the sudden changes in temperature in the case (taking it into the cold and then back into a warm, home environment) caused enough condensation to cause problems. Nowadays I wrap a computer in plastic before taking it to the customer. I haven't seen the problem since (about 80 builds later). If you have access to a de-humidifier it may be worth running it in the room that the computer is in, at least to begin with and see whether it makes any difference. I think you ought to be looking for an unusual solution since you've covered most of the usual points. Issues where a computer is unstable during warm-up are usually due to dodgy capacitors and/or PSU.
I never thought about it, that is indeed a good idea. I'll try it for sure later. It's winter down here and the temperature inside is like 18C and I never took the pc outside.
How long have you used this computer for? Have you used it regularly and then this problem occurred out of the blue? Did it just suddenly happen and has been this way ever since, or did it get steadily worse?
It's been 3 years. I used this computer without any problem and suddenly this problem happened. This problem has been this way since its first appearance.
Instead of booting Windows, can you boot into memtest86+ (http://www.memtest.org/) from CD from cold and see how works from there?
I did a memtest86 from a CD about 2 weeks ago. It passed all exams and found no problems with RAM.
Do you think if i overclock my cpu its idle temperature will went up, cause maybe that will prevent this problem temporarily.
Thanks so much for your help.