IS there a profile saved in the CMOS (BIOS) that will restore the OC?
EDIT>...crossed posts...
Do you know of any reason that might of happened? I've never come across a computer to just loose its OC like that... especially considering it's a very mild OC.Dodgy battery?
You have somehow hit a ClearCMOS button somewhere on the board if it has one?
If it is the battery, then they can be got from a supermarket for a £ or two.