Run fdisk. Preferably, boot from a Win95 (DOS 7.x) floppy with fdisk on it. Preferabley, set the drive as master and no other drives attached. Fdisk will tell you if you actually have a working drive and you can view the current partition table.

Even if the drive is fine, if there is no valid DOS partition found, or no logical drive in an extended partition, Windows won't see the drive. If fdisk sees the drive, delete any non-DOS partitions and create a DOS partition.

It's best to delete any existing partitions and remake them anyway, because different motherboards can have very different ideas about how to configure the drive.

If you have some weird partitions that fdisk won't delete, use the DR-DOS or Linux fdisk. If the partition table is totally screwed (some viruses will do that), you might need to 00 out the first sector with a disk editor. Fdisk will then make a new partition table.