PC get Restart

Dear Sir,

I have a peculiar problem. I am running on Win 98 and use IE5.5. When ever I start any of Internet Tool like Outlook express, IE, Messengers or anything, in 50% cases My computer get rebooted. It is costing a lot of corporate time. Please help how should I rectify it.

I do not want to loose any info and do not want to format my Hard disk. That is for sure.

Thank you
Arvind