I have a desktop system running XP, AMD Sempron. When I power up the system it appears to pass post, I get one beep, and sometimes make it to XP splash, then all of a sudden it shuts down. I have tried to go to safe mode, and even last known good. It gives the option and then again just shuts down for no apparent reason. I have also tried to swap power supplies which did not do any good either. Any suggestions are greatly appreciated!!