Could be many things. Depends largely what sort of user his son is. Typically, the number of items in "startup" under "msconfig" I've found to be a likely culprit; teens often download and install humungous numbers of programs, the other very likely culprit is spyware/adware and trojan-type nasties. If this is the case, doesn't matter how much the disk is defragged, won't make much difference. A good cleanup is probably indicated.