corrupted splash screen after re installing the system

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http://askubuntu.com – I've just installed ubuntu 11.10 on a 64bit machine with 2 nvidia cards. After installation, I rebooted and a black screen showed up, with a blinking white underscore. So I re installed the system, giving nomodeset as kernel boot option (since i understood it can solve this issue). Now i dont have a black screen, but a corrupted splash screen with no login menu. CTrl+alt+F4 does nothing. (HowTos)