Letter K was used once and I am unable to obtain it anymore.

I use P-ATA drives exclusively with a P4P800 ASUS MB. I temporarily hooked up a S-ATA drive after having modified BIOS settings to accommodate both P- and S-ATA drives. My W2k-SP4 assigned K to the S-ATA drive. Everything worked fine.

When I removed that drive and restored original BIOS settings, there was no way I could recover K as an assignable letter. It would never show up in the choices I had.

Tweak program did not show any hidden drives from A to Z.

Is there any way to make K available again?

From Windows Help:
To map a drive letter to a network computer or folder

Open Windows Explorer.
On the Tools menu, click Map Network Drive.
In Drive, select the drive letter to map to the shared resource.
In Folder, type the server and share name of the resource, in the form of \\servername\sharename. Or click Browse to locate the resource.
Notes

To open Windows Explorer, click Start, point to Programs, point to Accessories, and then click Windows Explorer.
To reconnect to the mapped drive every time you log on, select the Reconnect at logon check box.
Mapped drives are available only when the host computer is also available.
You can assign a mapped drive to a different drive letter by disconnecting from the drive and then remapping it to a new drive letter.

The letter K reappeared all of a sudden without my doing anything special.
I now have a red X under letters U, V and W which I do not use for the time being, when running Tweak UI. I assigned X, Y and Z to my DVD burners. They work fine. Red X disappeared from K.