- if windows hangs on boot process and doesnt show the starting windows screen , try safemode. It will show all the files that are succesfully loaded and hang at the last one.
if Mup.sys is the last one, then you might have hardware issues.
First run the recovery console using the WinXp istallation disk press R, logon to your partion and run scandisk or chekdisk maybe using the repair parameter.
if it founds errors you should run fixboot to make shure the boot sector is ok.
if any of the files are mising or corrupted you have to recopy them from the istallation disk or an existing windows os that is knonw to work.
i also recomend reseting the BIOS and make sure the acpi and anyting else related to power management is enabled. you can also try takin out 1 memory module and the video card if present or just swap the memory from their dimms. this will force the bios to update the configuration.