Windows 7 Random Reboots no BSoD

It crashes when I run with just one memory stick. I will try the Prime 95 and the DPC latency today.

ickymay said:

what result do your get trying my two suggestions here ??

I have solved my problem But will come back with the result of prime95 and DPC Latency checker.

It was the BIOS setup for the RAM. Before it was set to "Auto" in both speed and voltage configuration. I changed it to "Manual": 1333Mhz, 7-7-7-20 and close to 1,7V (http://www.valueram.com/datasheets/KHX1333C7D3_2G.pdf), runned memtest86+ with success.
Then I went into windows, created a bat file opening 40 youtube windows' without problems. Then I closed them all and put the pc in hyber sleep.
Opened it again the day after (today), runned the bat file, closed them all, opened other flash related stuff through the browser, with no black screens'n restart.
For now I'm happy

I have read a lot about the problem. It can also occur with C1E enabled in the BIOS or if you have an ATi R57** series graphic card (that I also have...MSI HAWK). It should be the ATi drivers fault, but they should have fixed it in the newest ATi driver. I'm running MSI's driver, with success.

Here are some other threads, that I found useful or have read:
ATI Confirms 5700, 5800 Problems; Promises Fix
AMD Game Forums - HD 5770 and screen flickering in win 7 desktop
Completly Random shutdown of windows 7 Professional. no BSOD, no Error Code upon restart.
GA-P55-UD3R Random Reboots - Gigabyte - Motherboards-Memory

Hope it also will work for you.
Best regards
Kenneth