Bridgeport 2000 V2XT (DX-32) Drive Enable drop out problem

I have a Bridgeport V2XT Knee mill (year 2000) with original DX-32 control.
Used to work fine, but recently have an issue where it suddenly acts like the drives are not enabled any more.
When it happens, I can hear the "thump" when the drives loose power. So far its always happened when the machine is not moving.
After it happens, the software still thinks the drives are enabled, but no attempt to move the axis has any effect.
The DX-32 software itself becomes a bit sluggish in certain places as a result also.
The only way to restore it is to reboot.
Has anyone seen this problem before? Id like to get an idea of whether its likely to be BMDC board, or the PC?
I tried reseating the BMDC and cleaning the contacts, and putting in a different socket on the motherboard.
Thanks for any ideas.

Get a DMM and check at the power to your hard drive. Check for VDC from black to red and from black to yellow. Black to red should be between 5.0 to 5.2VDC and black to yellow is 12.0 to 12.25VDC.

Are you running on a phase converter?

I am guessing it doesnt throw any alarm when this happens? When you turn the control on, do you have to press any buttons to get it to cycle through DOS and to the OS or does it boot up without needing that.

Jon