Sapphire R9 270x artifacts and coloured screen crash when NOT gaming.

Hey everyone!
I recently got my gaming PC. I chose the parts and it came with no software because I already have one. I installed the latest drivers and played for 3-4 days and then my problems started.
I had some black screens while gaming, and some artifacts-->coloured screen crash while not gaming.
Flashing my bios fixed the former but not the latter.Let me be more specific.
Every time, before I crash (vertical or horizontal coloured lines-one color full screen) there is some flickering on the screen and some artifacts. This happens after I hang around in my desktop or my browser doing stuff but it happens way faster if I do this AFTER I have played a game (1 hour, 4 hours doesn't matter). Since I noticed that it never happened while I was gaming (at least after I flashed my bios) I tried this twice: the moment I saw the artifacts I opened a game (Bioshock infinite on ultra settings) and played without a problem for a few hours. Then of course after 10-30 mins of browsing the web it crashed again.

I have tried these so far:
-Uninstalling and installing the drivers (tried latest stable from AMD's site, latest beta from AMD's site, the ones in the CD that came along, the ones in Sapphire's site. Nothing worked).
-Flashing my mobo's bios (fixed some problems but not all).
-Unplugged and plugged the cables.
-Putting the correct version of the driver in the registry (read on a forum that it helped in some cases).
-Checking the temperature seconds before the crash-everything seemed normal at 37ish.
-Downloading Trixx and checked unchecked some boxes (can't open it right now)

The reason I can't open it is because right now I have uninstalled the drivers again, so I could use my pc and post here. WIthout any drivers I don't have any crashes.

Here are my specs:
Windows 8.1 64bit
Sapphire R9 270X 2GB
MSI H97 Gaming 3 (1150/H97/DDR3)
Intel CPU Core i5-4460 (1150/3.2GHz/6Mb)
Corsair VS Series 650W
2xCrucial RAM DDR3 4GB Dimm 1600Mhz
WD Caviar Blue WD10EZEX 1ΤB HDD 3.5"

Anything else I should try before RMAing it? Is it 100% gpu's problem? Can I flash gpu's bios, too?Should I get a stronger power supply?
I can't try other gpu's or try this gpu in another pc, but I have tried other monitors and other connections (vga, hdmi) but the results are the same.

The best way to recreate the problem is this--> play a game for a while (play without a problem even for hours) -> exit game -> do stuff (paint, word, chrome)-->artifacts-->crash-->hard reset-->crash if you do stuff again except if you play games again then no problem.

I find it very weird that it has no problems gaming but it has with other stuff. Here's an album with some of the things I describe above http://imgur.com/a/XGG2J
the last screen is when artifacts happen, the first two is the crash (imagine it with orange or green,horizontal or vertical lines or a black screen)

EDIT: It just happened while I was trying another game (watchdogs) but instead of crashing, the game closed and I got a message that AMD's driver's failed and have been restored.