I just recently had a similar problem on an IRC5. For us, the solution ended up being that one of our three phases of 480 was slightly loose, and the controller was rebooting to protect itself.
So I guess check your 480?
Not sure if you resolved your issue but I had a similar problem that teach pendant kept doing its start up count and not stopping. I tried warm starts over and over. Finally came down to my teach pendant was failing. Not sure why. I swapped with another teach pendant. Being plug and play and a warm start later it did its normal start up count and never had problem since.
I changed the joystick and tried that teach pendant again and it worked fine on multiple s4c+'s. Lucky or good I'm not sure but it worked that time. 
I can confirm that problems with the TP can end up with the problem you describe.
Sent from my SM-G925F using Tapatalk
I've had similar problems when the pendant connector gets "wrenched". Unfortunately, the connector design makes them susceptible to damage.
I've also had image files get corrupted - the recommended solution was to delete the corrupted file and let the system rebuild it.
Check the connections on the computer. there is a Rj45 connector that sometimes gets a bad connection on our robot, there is a led right next to it that should be green, if it turns red, it won't boot up and counts forever. Sometimes rebooting works too but i usually move the cable around a bit and it fires up (after rebooting of course)
