I would say the symptoms could certainly be explained by a failing HDD, but sometimes you just have to use the suck it and see approach and slap a new bit of hardware in to find out. You may want to contact HP ASAP about getting physical restore media for that unit if you haven't already, because odds are it's on the HDD that is now going bad. It's HP so it's probably even money, at best, if they even still have the restore media for a unit that came with Vista, but the longer you wait the less likely it is. They'll probably charge you a small shipping and handling fee, but it's better than having to go out and buy a copy of Windows at full retail price.