Ubuntu tech, need help!

[kiwi_2005]

I boot into ubuntu 9.10 today tells me i have 47 new updates so download and install them, then restart and on booting up ubuntu i get this error:

[125.300362] Kernel panic - not syncing: VFS Unable to mount root fs on unknown-block (8,5)

I restart and this time choose 'recovery mode' At the end of the loading I get same as above & this one last then it just sits there:

[125.297688] no filesystem could mount root, tried ext1, ext2, ext4.

Anyway i can fix this without reinstalling the OS. I have Winxp on C and worried a reinstall might mess up the boot loader - where i could lose XP.

edit:
Ive put this up on the ubuntu forums but the threads move down the page so quick that its probably going to get lost in cyber space sooner or later.

Maybe i should just bite the bullet and reinstall Ubuntu as i think ive seriously screwed it up this time.