Is this a newly-installed or recently installed drive? I'm trying to find out if the drive worked perfectly until today...or whether today is Day One for using it as a secondary drive.
First thing I would do...check all connection to motherboard, power supply from drive.
I would also check Event Viewer, keying on any error which mentions "disk".
Is this a USB-connected drive...or connected directly to the motherboard/PS?
I would also attempt to run chkdsk on the drive, following the instructions for using the graphical version, XP Chkdsk, Using the Graphical Version (My Computer) - http://www.updatexp.com/windows-xp-chkdsk.html
Put check marks in both options (Auto fix and recover) which appear when you click the Error-Checking button.
If the chkdsk is unable to complete (not what we want, but a possibility), I suggest immediately downloading and using (per instructions) a diagnostic program from the website of the respective hard drive manufacturer.
Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp. - http://www.tacktech.com/display.cfm?ttid=287#samsung
Hard Drive Installation and Diagnostic Tools - http://www.bleepingcomputer.com/forums/t/28744/hard-drive-installation-and-diagnostic-tools/