Hello and welcome to Bleepingcomputer.
From reading your description I believe you're saying you can boot from a boot disk in the floppy (A:) drive, but it is not recognized by Windows 2000. Is this correct?
I will reply with both possibilities that it is not being recognized by your system and Windows 2000, so that both possibilities are covered.
First you should enter your BIOS setup utility and see if there is an A: drive listed in the main BIOS utility screen.
If A: drive is missing, you will want to shut the computer down, open the case, ground yourself to the computer case and locate the ribbon wire which is attached to the floppy drive.
Next unplug this ribbon wire from the floppy drives data connector and plug it back in again. Do the same to the connector on the motherboard.
Make sure the small 4 wire connector wired to the PSU is connected tightly, or do the same as you did with the data cable.
Try booting up the computer to see if the drive is now listed in your main BIOS screen. If it is, then exit the BIOS and boot to Windows and see if the drive is now listed under my computer with-in Windows. If it isn't then the drives controller board has failed or the data cable is faulty, try using another data cable to see if problem has been resolved.
Floppy drives do get dirty read/write heads, opening the drive to clean the heads with iospropyl alcohol and cotton swab may be needed. But this will not prevent the floppy drive from being recognized by Windows.
If replugging the data and power wire do not make the drive appear as A: drive in Windows 2000's My Computer, the controller on the floppy may have failed and a new drive will be needed.
Please post back and let us know if the above has helped in any way.
Edited by MrBruce1959, 01 July 2010 - 08:59 AM.