Diagnosis
Total power loss is almost always in the supply chain: the outlet, the power cord, the internal fuse, or the main control board.
How to Fix It
Start simple. Check that the 115V outlet in your crawl space is live—plug in a lamp or tool you know works. Next, trace the power cord from the unit to the plug, looking for any cuts or chew marks (critters love wiring). If that's all good, the next stop is the internal fuse. Unplug the unit. The fuse holder is usually on the lower right side of the cabinet behind a small, removable plastic cover. Pull the fuse and check it visually or with a multimeter for continuity. It's a standard 5x20mm glass fuse, often 5 amp or 6.3 amp.
If That Didn't Work
If the fuse is blown and a replacement blows immediately, you have a short circuit inside—often a failed capacitor or a wire rubbed through. If the fuse is good, then the main control board or the wiring harness from the power inlet to the board is likely faulty.
Heads Up
When checking/replacing the fuse, make absolutely sure the unit is unplugged. And if you're not comfortable with electrical diagnosis, this is the point to call a pro. Crawl space wiring can be its own special nightmare.