hi, had this happen 3 times in 20 days after installing my R9 270X:-
I've used a tool to completely remove ALL Nvidia AND AMd drivers from my PC, then reinstalled the latest non-beta release from AMD. also removed a syswow64 driver that kept generating errors that coincided with these crashes, only just done this last bit so dunno if it'll make any differences.
This issue ONLY happens when the card is pretty much idle, never happens during games only when im idling on youtube later on at night.
Been speaking to my supplier about RMAing the card if I can't get it working, it's still within their warranty (in addition to AMD's warranty so shouldnt be an issue).
Has anyone seen this before on the R9 270X, or better yet know any software fixes for it?