i show this in corp it class on how to lock yourself out of a pc in 30 sec. when you boot the os reads your cmos info and puts it into a file and counts down till the date windows will expire. when you roll back the date that little program and file go gotcha and lock you out of your pc. even if you put the date back you be screwed. you have to reinstall windows and you may lose all of your data on the pc. if your low on cash your better off looking to see if yur school in the windows edu program or look to ebay for oem copy of windows.