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Since I've installed ubuntu 12.04 I have this problem (on mint 13 I also had this problem) now I have ubuntu 12.10 updated and windows 7 with it.
When I go to windows everything works fine but some times suddenly if I choose ubuntu, it will stuck in violet screen. Even the login screen wont come and I should press and hold the power button to reset my laptop I have to do this for 3 or 4 times.
After reseting and choosing ubuntu again a black screen come and there is a dash in it and nothing else. I'm woried about my lap top . if I reset it again I'm afraid it could get serious problems.
My laptop is hp probook 4520s 1GB swap space.