Install "end it all" from http://home.ptd.net/~don5408/toolbox/enditall/
Use this program to turn off all your running programs, than defrag. You can shut down everything including the locked files, the program will not let you shut down any necessary windows programs. This will allow you to defrag without any interruption.
I have been running W2000 for a couple of years now, and this is the second time I have had this problem.
Background info is: Running a PIII at 750Mhz, with Windows 2000 with virtual memory nearly at max, 256M RAM.
Today I defragmented for the first time after formatting, and, just like the last time I did this, if I leave my puter idle for any length of time, it refuses to respond to either the mouse or the keyboard, and the only solution seems to be rebooting from the button on the tower, as even control, ALT + delete has no effect at all.
Anyone out there ahve any ideas.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic