You do not want to wait till the hard drive fails completely to try to set up your system from scratch on a new hard drive. I had a hard drive failure (with warning) last spring. I thought I was in good shape with backups, installation CDs for my software, etc. but it turned out that if my old drive hadn't woken up long enough for me to retrieve all the files I could from it, I might not have been able to get my system working fully.

Rmdctc's suggestion, to take it to a repair shop, sounds like the easiest way, but better do it before the drive fails completely. If they're really good (and your old drive cooperates) they should be able to "clone" your old drive to your new one. If they're not so good (or your old drive quits early) you may end up with a working Windows system but minus a lot of your software and data.

If you want to replace the hard drive yourself you'll need to start by finding out what's in there now and how it's connected; as I understand it there are two kinds of cables in use called SATA and PATA and you'll have to stay with drives that fit what's in your computer. If you didn't know that (I didn't, till last spring), the learning curve gets even steeper after that.

I've never had an HP but for my Dell I was able to download an instruction manual that described how to get the case open, how to change the CMOS battery, how to add a hard drive, etc., etc. I'd printed off the manual a few days after getting my computer (used) and I had it handy in a binder to refer to. You might want to do something similar while you still have a working computer.

One last thing -- I don't think I would've made it through my system reinstall if I hadn't had a junky old spare computer that I could use for going online till my main one was working again.

Good luck, PlanningtoLive!