How far does it actually bootup? I know if you have a illegal or generated product key, it will ask you to enter a valid product key and if you don't you will be locked out, if this is the case get a valid key. If this is NOT the case try hitting F8 while windows is booting and select SAFEMODE from the options, try to see if there are any major problems with HW compatability etc. If all else fails, and you can get in SAFEMODE, uninstall the SP. HTH