Hi there. Well haven't been there yet but if I were you I'd put the card and enter safe mode before windows loads, uninstall from control panel all catalyst drivers and then re start. That way you should be able to do a fresh install.
Thanks for the replies. I was just worried it will be awkward. to enter safemode, do i hit f9 when computer is turned on? Iv never had to do it before? And i am getting a new 680 card so fingers crossed, all will go well