Typically No power/Low Voltage is a wiring connection or dust obstructing the optic sensors, or a faulty sensor. After clearing the obstruction the lathe may need to be reset.
The picture illustrates the connections to check.
There are three files attached. The first two are relevant to your symptoms.
FAQ DVR POWER FAULT INTERMITTENT 6 pin molex is a troubleshooting document. The other two explain how to remove and replace the control panel and main board.
One factor that could be pertinent. Older DVR 3000s (serial number < 8000) have a different style board and heat sync, and some older models have a power filter. Please note if it has either in future communications.