Just installed 12.04 (fresh install). I had remove my second HD for safety reason (The two drive are exactly the same - too easy to mix up- been there done that).
So, all my personal data is on this second drive but when I reconnect it and boot, the computer (HP8020N) will not reboot. I have tried different combination (moving the HD on different SATA on the board, removing the DVD) to no avail.
The best I got was a purple screem and no more. Both drives and DVD were working flawlessly before on 10.04.
It is possible that this is a new hardware problem but I doubt it. The second HD has only data on it, no OS.