Restart and hold the Shift key until you see the Apple Logo if it starts up OK restart normally. Let me known is there is any change.
That seems to have one the trick - thank you very much!
I just rated your answer excellent - which it was - but have since found something that doesn't seem to be working as before. Can't get any sound now. Itunes doesn't play for example. The volume keys on keyboard not responding.
I don't know. I don't think I'd be comfortable removing anything... not very technical!
Should I disconnect my external hard drive before I do this?
Thank you so much! Sound back on now and everything else looks to be okay. Thanks again!