X locks up

[tracheotomy bob <bob@gonzo.spoiler.demon.co.uk>]

I've got this strange problem with X, occasionally after the screen 
blanking comes on, the system hangs when I move the mouse. The screen
comes back but nothing works, the keyboard is locked and best of all, 
so are the hard-drives. In fact the only way to get out of this lock is 
to hit the reset button. However...at this point neither hard-drive is 
visible, the lights are on but they're just freewheeling. The ONLY way
to cure the problem is by physically disconnecting the IDE cables from
the drives.

I suspect that this is not normal.

If anyone has any suggestions I'd appreciate it.