Trotter said:No, you don't have to reformat, but you do have to remove any and all traces of ATI drivers.
Uninstall them, them search your hard drive for any stray bits and pieces, them scour you registry for anything.
ATI and nVidia just don't get along at all.
well, for me that didn't work, i cleaned out everything i could possibly think of, until there was no trace of ATI, and still dind't work until i reformated... but again, that's just me