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.
First probability is a BAD CONNECTION. Unplug the power and remove the four screws to the control panel. Check the control panel connections to the interface board. Unplug and replug both ends of the grey ribbon cable from the interface board to the keypad panel, and from the interface board to the main board. Retest with power.
If necessary, open the headstock and with a meter check the black and white single power connections to make sure you are getting 110-115VAC. Examine all of the 4 sets of connectors pictured, especially the 6 pin molex. It may have connectors inside the plastic that have expanded with time/heat/fatigue.
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.