custom, pop in your windows XP disk while your in windows, do an install, u can do an "update" install and that will keep all your programs, but if u dont mind loosing all your programs and stuff its best to do a fresh install, it will take about 30 mins and its not that hard to figure out how to get it.. try that and it will fix everything and your computer will be back to how it was when you bought it. if xp messes up and doesnt install some of your drivers go to
http://www.driverguide.com (i think) the login/pass is DRIVERS ALL
second person: try messing around with the S.M.A.R.T thing in your bios and all the other harddrive settings and IDE settings, also check to see if the harddrive is on master or slave, dont use C select it never works =\.
hope that helps, if its an emergency call my number in my sign