I have the gray/blue-line crash before. and I found out it's my 1000W PSU problem. The PSU 8Pins PCI-e connection can't provide enough power or the voltage is not stable(it works fine with my old 2x 4870). My 5970 had gray screen crash frequently. I just replace the PSU 8pins PCI-e connection with the 2x5pins to 8pins convector and my 5970 works fine! no more grey crash or random crash!