I have a Late-2011 Macbook Pro (4GB RAM) that has been running slow for several OSX cycles, and since Mavericks it's been unbearable (spinning beachballs whenever you do anything). I tried upgrading to Yosemite hoping this might improve performance; no dice. I've decided to try clean-booting Yosemite to see if this improves things.
I've been following instructions here to do a clean install and here to create a bootable flash drive. Drive creation seems to work fine: it has the correct GUID partition table, terminal command exits with the
copy complete; done output, the disk shows up in the Finder as "Install OSX Yosemite", etc. When I restart the computer holding Option, the installer shows up as a bootable disk (unlike the question here).
My problem is that when I then click on the installer, I get a loading bar for some seconds and then the screen goes to a circle with a slash through it. It's the same behaviour detailed here but note that I have verified that my disk has the correct GUID partition table. I also tried resetting PRAM, to no effect.
Any suggestions welcome.