I installed Ubuntu 9.10 and things were working fine. Today however my laptop will not boot. It shows me the GNU GRUB screen asking me to choose between any kernel version 2.6.31-[14, 16, 17, 19]-generic both normal versions and "recovery mode" versions (before it chose one of these options automatically after a few seconds).

If I choose the non-recovery mode kernels (any version), it eventually gets stuck in a black screen. After pressing any key, I get this message:

Gave up waiting for root device. Common problems:
... ...(shows a list of three common problems)
ALERT! /dev/disk/by-uuid/(a long id) does not exist. Dropping to a shell!
BusyBox v1.13.3 ...

If I try one of the "recovery mode" kernel versions (any and all), I get the same message but the last few lines printed out before this same message are:

Begin: Waitin for root file system... ...
Gave up waiting for root device. (etc.)

Thanks in advance for your help.