M17xR3 Random black screens - Please Help !

Hi everyone,

I have a big issue with my 17xR3 bought some months ago. I'm getting random black screens after Win7 loggin, while playing games or just when searching on the Internet. Each time I get a black screen need to do a hard reset : lights and CPU fan are still on, but laptop is locked up. When I first bought the laptop, everything was fine for at least  2-3 months. Then I started getting one or two black screens a week, and now it has reached an unbearable limit as I can get up to 10 black screens a day (the fact I don't use the laptop for hours doesn t have any impact).

I tried various nvidia drivers (old/newest/Dell ones), clean install or sometimes even cleaning with CCleaner/DriverSweeper ; without success.
I tried clean boot, deactivated all non-MS services, deactivated antivirus (MS essentials) and firewall - all in vain.
I tried to check for minidumps, I most of the time don't get any, but when I get one, it's a bugcheck 0x117 (directx/or nvidia driver/or hardware issue). Directx is up to date and shows no conflict according to dxdiag.
I checked fans : no dust problem, room temp is 22 C ; to me this is not an overheating issue (black screen can occur when I'm not playing games, and GPU shows a temp ~55 C under Windows as per Alien Autopsy and Nvidia drivers on).
I launched Alien Autopsy checkup tests : all are successful (even GPU ones).
Also used SFC/Scannow, Memtest : no issue.
As my laptop supports 3D vision, I don't use Optimus/integrated graphics.
I configured the laptop for Max performance under Windows, and I'm never relying on the battery.

I noticed that in safe mode, or if I switch from Nvidia drivers to standard VGA graphic adaptor, issue disappears... no more black screens.

But my ability to play games disappears as well, which is quite frustrating with such a laptop.

I fear the issue is hardware/graphic card related (or motherboard ?) - could be a nvidia chipset defect - but why would the pb start after 4months ? What is all the more frustrating is the fact that in games the laptop is performing well (GPU is providing nice images, fan is adapting well, temp never going above 65 C) but the experience is ruined by those random black screens... that I can even encounter without playing games.

If anyone else has an input on this problem or can provide some help - Alienware owner or tech support - would be sincerely greatly appreciated !

Thanks in advance

My configuration :
I7 2670QM
GTX 580M 2GB Bios 70.24.2b.0.6
16GB RAM
HDD 1To (raid0)
Laptop is 3D Vision compatible - 120Hz