Help: can't no more boot

[Pierre Frenkiel]

hi everybody,
I had since several days USB error messages (error -110), but all seemed
to work normally. This morning, I got a lot of these messages, and 
"lsusb" froze my terminal window. I decided to reboot, and I'm now
stuck at boot, with messages:
     Gave up waiting for boot device
     ...
     UUID_of_device   does not exist

     and I get a busybox prompt: then, I see that  /proc/modules is empty

     Booting from a USB stick, I mounted the partition without any
     problem, and checked that the UUID found in /dev/disk/by_uuid corresponds
     to the one in menu.lst (anyway, replacing the UUID by /dev/sda2 gave
     the same result: "/dev/sda2 does not exist")

     How can this happen?

     PS: my Ubuntu version is Intrepid.

-- 
Pierre Frenkiel