Alright, I had a mysterious ticking noise in my hard drive, and, after two and a half HOURS online with tech support for HP, they determined it was "bad," and sent me a new one, since I'm still under warranty. I then installed it and started system recovery with the recovery disks they sent me.

Thirty HOURS later, system recovery still wasn't done (and I'd restarted the process twice, with the approval of tech support, before I decided I had to fight back). Finally, I simply MANAGED to get past the full-screen "please wait and don't shut down your computer unless we TELL you to" screen, and was able to use my computer, since it's kind of vital to my life. Recovery seems to have stopped now, but my computer is working great.

My real issue here is that my 500GB hard drive seems to think it's only 50GB or so. I am running Windows Vista on an HP Media Center PC, and my hard drive thinks its half full already. How do I FIX this?Maybe the remaining portion of your harddisk isn't yet formatted. Check if that's the case. On your dektop, right click "My Computer" icon, then choose Manage. On the Computer Management window, click Disk Management under Storage and check if there's a PARTITION that hasn't yet to be formatted. Keep us posted if you were able to work your way through.
Goodluck! Did you reinstall your motherboard drivers?The 2 prior answers are very good, but check your BIOS. Sometime the LMB in the BIOS will not detect/read a HD so big. U might need to upgrade the BIOS.