I'd look at the battery too.
You may want to install some software that keeps your computer on time by synchronising it with a time server. Check out AboutTime:
http://www.arachnoid.com/abouttime/
You'll also need the address of some local public time servers. Try ntp2a.mcc.ac.uk, ntp2b.mcc.ac.uk, ntp2c.mcc.ac.uk and ntp2d.mcc.ac.uk - all in Manchester.