white screen, safe mode won't boot up

My iMac won't boot up in safe mode (shift key) and when I try to run Recovery HD (option key) I still get the white screen freeze up.

Order of events:

computer was freezing with vertical lines, sometimes on boot up too.

Tried installing avast. Now vertical lines every attemp to boot up.

Reset PRAM. now white screen freeze up on boot up

Safe mode (shift) results in white screen

Recovery HD results in white screen

So nothing appears to be loading, except the single user mode.

Is there anthing I can do in the single user mode to revive the beast?

Thanks!