Go into your BIOS at startup. Find the option to "load setup defaults" or something of the like. Then save the changes and reboot.
Then, in XP, go into start, settings, control panel. Go to administrative tools. Go to computer management.
On the left side, go to disk management.
At the bottom, there are 3 bars. On the left of each bar it will say Disk 0, Disk 1, etc. On the right side will be a bar with diagonal lines. On the left side, right click on the diagonal lines to the right of the Disk # that represents said drive. Click "Mark Drive as Active."
Give that a shot...I recently had similar problems...