Hi!!! This is a real good one..... Things that can cause endless rebooting: Overheating, spyware/virus/adware, PSU, VideoCard, Conflicting Software-running in the background. (I've heard of some new internal card reader causing endless rebooting- but can't confirm). Possible virus maybe, with the two different type installs- unusual. I've even thought about insufficient RAM causing endless rebooting, it kills a lot of XP memory. But it wouldn't have these symptoms. (Compaq Evo, runs hot, hard to install Vista). Have you talked to HP Total Care?

__________________
Celestra