you need a windows start up disk, go into prompt, since the drive is being recognized, then fdisk the specific drive.. I would UNPLUG your current one, JUST IN CASE, so you dont fuck the wrong drive up.
1) Turn PC off
2) Unplug main hard drive
3) stick startup floppy into disk drive
4) boot up
5) load into command prompt
6) fdisk the drive back to FAT32 or NTFS
7) format it
8) take floppy out
9) restart
10) verify drive is working - you shouldnt see anything since its empty, you'll get a NO OPERATING SYSTEM error most likely.
11) Turn pc off
12) plug main hard drive back in
13) boot up
14) done
DOWNLOAD A BOOTDISK:
www.bootdisk.com