Thanks Rik, by checking the Event viewer I was able to get a little bit more
detail. I am going to try setting the IPSEC Service, in Services to manual
and see if this fixes the problem. I read online about others with similar
problems and this was caused by IPSEC Services. Apparently, XP firewall and other Security firewalls running at the same time may cause some problems, such as mystery reboots when this service is enabled.

Well there's only one way to find out.

I'll let you know what happens.

As to this being a worm/virus, I don't think so as Spybot and NIS have not
reported anything after scanning

Thanks
halder