unclean shutdown

Help Me

I can not get into Ubuntu, (and I am having to use windows :-( )after the loading screen I get check with the message of
Unclean shutdown., checking drives;
/dev/sda 1...
it gets to 86% and then goes into another screen with a lot of writing.
Sorry I did not get it all but this is what it says

A automatic file system check(fsck) of the rootsystem failed
A manual fsck must be performed.

and somthing about in a read only mode.
then
/dev/sda 1 : unexpected inconsisency : run fsck manualy (ie., without -a or -p options)
fsck died with exit status 4

How do I fix it can I do a repair like that of XP (sorry about the windows wording).
Or will I have to reinstall?
Thank
Neil