Did you replace the original power supply when you replaced the C5c?
What caused the other one to loose power?
Will the original C5c boot off of another power supply?
You might want to check the cable as well to see if there are any breaks, one time I had a customer weed wack his cable and then called us with weird intermittent issues. I eventually gave up trying to diagnose it remotely and only found the issue because I dropped a tool off of the roof. Two days of diagnostics and three hours of replacing and trying out various antennas on a roof taught me a very valuable lesson. To quote my cousin who does networking for the Air Force “always check Layer 1 first.”