In the fisrt place, I apologize for my poor english.
Here is the matter : I ordered sixteen months ago on Dell's website a Vostro 3700, which I have used since then for my personnal use as much as for work needs, and which has worked absolutely fine for me one year long. But then it began to shut down after 2-3 seconds of an abrupt black screen when too much used with heavy applicatoins such as games or video creation software. I first suspected overheating, and that's still my guess today.
I soon bought compressed air sprays in an attempt to get the fan unblocked, but saw no dust coming out (indeed I saw later that this was not the cause, since the fan and its grid seem almost perfectly clear). Then I tried with thermal paste. I opened the computer following the instructions on the site (using my service tag) and saw that there was paste over none of the chips, but all around. So I tried to gather it and put itback on the CPU and the GPU. The Vostro began to work fine again form here, for approximately one month. I bought some new paste, removed everybit of the formerly used one, and replaced it (forming a fine layer), which got me a few days.
Then I saw that the paste I had added had undergone the same movement as the prior one, i.e. it hadn't stayed on the chips but had slided around (or what hat staid on the chips had dissolved or whatever). I began to wonder whether it wasn't simply too hot within the computer, so I bought a cooler pad, a seemingly good one with three fans that I placed where the computer heated the most (CPU, GPU/fan, and in a lesser way the hard drive disk). Two months long I sensed my PC heating but not overheating anymore, and yesterday it happened again, two times in a row. I had let the womputer cool between, and had also upgraded my BIOS from version ??1 ton ??10, just in case, and followed the diagnostic at the boot which gave no error.
Here I'm just lost, and don't know what to do any more, so I'm waiting for your advice.
Thanks in advance
P.S : Come to think of it, Windows logs only shows the cores stopping activity when it happens. I don't have heavy applications enough on Linux so no log there.