El Capitan install goes White Screen
I have tried several times to install El Capitan on my 27" iMac, but each time it goes through the process I end up with a white screen. Rebooting at the end doesn't help either. Apple Tech Support has taught me how to restore from my Time Machine with Command-R and made suggestions of what to try next, but no success.
I've wondered if there is some hardware that is not compatible with El Capitan since it is a late 2009 model, so yesterday I even took it in to the Genius Bar and had a very good Tech look at it. He cleaned out a lot of adware type softwares that have slowed the system down over the years, ran some diagnostics and found everything checked out fine. He explained a lot of these adware type programs were bogging the system down and were the likely culprit. He sped through the cleanup so fast I couldn't keep up but when finished he was certain once I got home and started the El Capitan install, it would work this time. It didn't.
He downloaded it for me at the Apple Store before I left, had me install it once I got home and the screen once again went white. Though he doubted it would happen, he suggested if I did then restart and install the OS X option after depressing Command-R, it should work then. So I did that last night and once again, white screen only. That led to this morning's only choice left, Command-R, Restore from Time Machine the last backup before going to the Genius Bar appointment and back to Yosemite 10.10.1, with 14.5 hrs. to go now before the install is complete.
There's only one clue that may be relevant or related. The computer freezes up on occasion, though the mouse is visibly moving around on the screen, mouse clicks and/or keyboard strokes suddenly have no effect, it's as if it's frozen in time. The tray won't pop-up when the mouse is moved to the bottom of the screen, no drop down menus will respond, even Command-Alt-Esc won't open the Force Quit Applications window. Only option is a hard reboot. This happens sometimes days or even weeks apart, but more recently more than once per day.
With diagnostics saying all systems are go and all potential softwares that may interfere with an OS install having been removed, does anyone out there know what is going on? I'm suspecting hardware issues, but so far Apple Support and Genius Bar have all said the same thing, it shouldn't be a hardware problem.