Can't install Yosemite

[Oldmanmac]

using my 2011 21.5" iMac on a usb flash drive. I have tried twice and both times it freezes about half way through the install. I left it for 48 hours this time to give enough time. Any thoughts?

 

[adam9c1]

How did you create the USB installer?

Can you scan the iMac HD for errors?

 

[Oldmanmac]

Just tried using the flash drive as a regular drive.