im fixing a friend's computer and whenever windows boots up it restarts suddenly right before windows loads. after it restarts it goes to the screen where there are options for booting windows in safe mode, normally, etc (windows xp). safe mode gives the same result, windows doesnt boot and restarts comp. ive tried reformatting the HD but it says it cant reformat. after seeing that the HD cant reformat, i bought a new HD and swapped HD cables so i know it is neither of those components. windows installed and loaded fine on the new HD but after using the computer for a day or so, the problem is back. the computer wont boot windows and keeps restarting when it tries to boot. any suggestions on what may be the problem?