Have a look here to do XP repair Install
http://www.michaelstevenstech.com/XPrepairinstall.htm you should lose no data but backup just in case. read carefully and follow instructions. To get safe mode you must press F8 repeatidley as soon as you boot, if it's not working, wait for Win to boot first screen then hit F8 as quickley as possible , you may miss it a few times but keep trying.