Ubuntu crashes during boot

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http://askubuntu.com – When I try to boot Ubuntu 12.04 it will crash and I have to restart my PC. I'm dual booting Windows 7, right now when I try to boot it gets to the purple screen but nothing shows up. It will stay on that for a minute then the screen flashes white then goes black and the screen shuts off(not literally just says no display device active) I've used Ubuntu before and never had these problems. This all occured after I installed ati video card drivers for linux. I'm also on 64 bit version. Please help and thank you. (HowTos)