PC is getting restarted Internet is ON

P4 2.4 GHz, 512MB double slot RAM, Intel Motherboard, Win XP professional. is the configuration of my system.

Question I know some general problems and solution of PC getting restarted. But on my Desktop its frequent thing while Internet is ON. Not able to scrutinize the problem.

If anyone of you have solution for this please hit back. Cz its very irritating while PC gets restarted when Net is on.

In advance Thank you.