Ubuntu stuck on boot

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http://askubuntu.com – When I start up or restart my computer, I see the gray underscore in the top-left corner, flashing as it should. Sometimes though, it just keeps flashing, and the system doesn't start. If I try to boot in recovery mode, I can see the text log instead. From there, it gets stuck at a few common points. Again, it's just stuck there until I reboot it. Anyway, this only seems to happen on Linux. It didn't happen with this computer under Windows 7. I've also had this computer for quite a bit, so I've already gone through plenty of AMD drivers and kernels. I don't think those are the issue. Any hel (HowTos)