Hi, I have a mid 2011 27" (3.4 GHz Core i7) iMac that as of last night is throwing up the White Screen of Death about a quarter of the way into the Apple logo boot up. I have tried booting into recovery, a Windows partition, and an SD card with bootable Yosemite ISO mounted to it... and the result is exactly the same, a WSOD about 25% into the progress bar. I have also tried single user mode to check for modified drives, I have reset PRAM, and I have attempted Safe Mode. Again, all with the same white screen and eventual reboot. I'm presuming/hoping that as a result of it being able to at least show me start up options such as Recovery and OSX/Win partitions, that the fault is more software than hardware. But without being able to gain access to Disc Utilities I'm up the creek! Does anyone have any further ideas? Thanks.