First of all, Welcome to TechIMO!
Now, when you are acutally in XP (I think you said you could boot into it) can you go right-click My Computer and goto Manage. In the windows that comes up select "Disk Management". There is a list there that shows all of the logical drives in the system as well as all of the physical hard drives. Does your drive show up as a physical even though the logical volume is not there?
If so, there's probably a problem with the partition table. If not, you may want to test the drive itself.
You could try booting to the recovery console and running fixboot, fixmbr, and bootcfg /rebuild to rewrite the partition table on the drive. You may also try doing a repair install from the XP CD (boot like your going to install a fresh copy of Windows and select repair AFTER it finds your installation).
If the recovery console can't even detect the Windows installation on your drive, try running a drive tester utility like
Drive Fitness Test to see if everything is okay physically.
I'll try to think of more ideas, post more questions if you have any.