No longer able to boot into Ubuntu!

[Andy Jarvis]

I shut down my PC last night after spending time on Ubuntu and 
everything was fine. When I tried to boot it up this evening, I 
received the following message:

Kernel panic: VFS: Unable to mount root fs on unknown-block (0,0). As 
the PC has not been used since I shut down last night, I can only 
assume one of the synaptic updates has caused a problem (I run smart 
updates every day). Either that or my hard-disk has mysteriously become 
corrupted at some critical spot. In case it helps I run the K7 version 
of the kernel.

Until I can resolve this problem I am very stuck.

Regards,
AndyJ