i think he means restarting after windows logo... i think three problems can be there [any one out of three]
1. first check whether windowsxp OS is not corrupt?...if not then proceed to step two 2. it can be a SMPS problem [not enough power supply to regualte or power not transfered to the extent required , a faulty SMPS can be the cause] 3. If SMPS is alright, then motherboard can be the issue, the capacitors may not charge/discharge properly, also it can be anythng on the motherboard as it is a big playground of small things]