Weird sudden Blackscreens

[mineplay011]

Hi,
i have a very weird problem, a week ago my computer started getting weird blackscreens (mostly during games), which would recover after 2 seconds or so (everything works fine after that but game crashed and AMD Software did too) but i havent changed anything. Now it seems so do it more often and not only in games... Whats weird is that i can sometimes play very demanding games like Crysis 3 on MAX settings with no problems and sometimes it crashes while using firefox and the explorer.
First i thought, that it would be the graphics driver, which i updated and later completely reinstalled but no difference up to now.
The graphic card doesnt seem to overheat as well.. is runs at its toasty 85-90°C in games as usual...

I used the RX480 now over a year without any problems and without any overheating issues, which the older GTX 660 had....

Specs:

Case: Alienware X51 R1 (the reason for top of the line temperatures)
PSU: 330W External powerbrick
CPU: i5 3330 @3Ghz non K

Ram: 16GB DDR3
Storage: SSD + HDD (both rather new)
GPU: XFX RX 480 Black Edition (mostly referenz design, just with backplate)
 

[mineplay011]

Well i dont have the GTR edition i have one of the first RX480 cards no custom design or anything, and upto now no power problems... the system stays on... and the card is only able to get 175 or so... just a six pin connector... like i sad one year and no problem at all

This is my card:
http://www.xfxforce.com/en-us/products/amd-radeon-rx-400-series/rx480xxx-rx-480m8bfa6

And it came stock with an GTX 660 with a TDP of 145W which is roughly the same.... it also would "require" a 450W PSU