yes I agree, you can change the harddrive yourself.
as long as you have all your drivers for sound card, video card, NIC card etc.
most of them you can get new releases from the vendors.
open your case up and find your harddrive, most of the time its right under your floppy drive, undo the four screws and slide it out, unplug the cables and look for the name on it. now if you have time you can try and locate the utilitys from the manufactor of the drive, exp if its a maxtor drive goto
www.maxtor.com, remember to right down the info from your HD.
you cant us maxtor tools with a seagate drive and vice versa, they have to be from the same company. however if it is a old hd and you want it fixed goto your local store and pickup a new drive. then open it up read the directions and install it back were the old one was. then pop your OS disk in and turn it on. format and install all your stuff again and there you go.