i'm working on an emachines running Win Vista. at startup it will go through post but as soon as it hands over to OS the PC shuts down. cleaned out case (wasn't too bad) problem still persists. i disconnected the HD and it will run all day. i ran MalwareBytes and got a few hits (i installed HD as a slave in my PC). many Adware.MyWebSearch instances, a Trojan.Vundo, and a Hijack.DisplayProperties. Will any of these cause the PC to shut down?
i am familiar with the bad PSU's used by emachines. this one is a 450W apower AGS series. it might be possible that it's not pushing enough power to run the OS.