I upgraded my 2007 iMac to Lion and after a few days of perfect running the thing locked up. When I forced the power off and back on it seemed to be booting fine (chimes, apple logo, disk spinning up and I could hear the drive head seeking) but then it froze up in the "White Screen of Death" (WSOD). It was completly lockd up again, and nothing would bring it back. I had to reboot again. And again. Everytime it seems to be starting ok, but then locks up after it the screen goes white. . I did command option , p r keys with three chimes. I have unplugged it and let it sit. I disconnected all periferals including my Time capsule. I reset the SMC. I booted into Single User mode and used unix commands to check the HD. No errors found. Note that it appears to be booting fine at first with the usual grey Apple Logo. And when I boot into the Single User mode all the text indicates no faults. The display and HD appear fine. I then replace both RAM chips. No change. I inserted my original OSX Leopard disk and and tried to boot from it, using the "C" boot process and the Option boot method to manuualy select the DVD. No good. It just went into the WSOD again. I inserted the Lion Thumbdrive that Apple sent me. It too started to boot as normal - but then after a minute I get the WSOD. I booted in using the "T" target disk mode. That worked, to mount the HD up on my Macbook. I scanned the HD and no repairs where needed. I then trid booting again. No luck. So I erased (and zeroed) out the HD and trie dto boot from the DVD again. Nothing changed. I still could not completely boot up the install disk or thumbdrive. Now I have a brick. A very large and heavy brick. I have no idea what to try next!