Kernel panic after upgrading Nvidia driver

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http://askubuntu.com – So I made a textbook error, and after I had got everything else working nicely on 12.04, thought I would try to upgrade my Nvidia drivers to "current", since that was recommended, in the hope it would improve 3D performance. Slight problem: I can no longer boot my kernel. The error reads, in part: Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) PID: 1, comm: swapper/0 Not tainted 3.2.0-31-generic #50-Ubuntu That's followed by a call trace, which I'd rather not have to retype by hand unless it's necessary. Recovery mode also does not work, giving the same err (HowTos)