Ubuntu 12.04 freezing on startup

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http://askubuntu.com – Have been looking everywhere to find a solution to this problem but have yet to find a solution. I am running 64 bit 12.04 LTS on a AMD C-50 Dual core 6 gigs ram AMD Ratheon HD 6250. The problem I am experiencing is when ubuntu gets to the wallpaper screen it will sometimes freeze soon after the the image appears or shortly there after gnome loads locking up keyboard and mouse. When I try to log in via the console the same thing happens (this is as ubuntu is loading). At the moment the system is set to auto login previously it was set to ask for password but it did the same thing. Switching (HowTos)