The Short Answer it is DEAD (for the moment), without that, an Electrician was onsite:
You killed your UPS due to a Voltage-over-Fault. (Coil Discharge Ignition)
The Main issue and cause is, that you can, even under nearly Zero Load, get and become Voltage Spikes that can kill any Electronics Inside. Specially Capacitors.
An Other Reason for this can also a Faulty Production Process, which may be Covered from the Warranty
A Third Variant is also Possible, SOME - but, not often of these ones have also a second Fuse, which is only Accessible by opening the CASE of the UPS - Remind, for this action the UPS should stay away from power for at least HOURS - Even then there could be Voltage on the Board!!
Remind if this not Solve the Issue, look for a RESET Procedure on your Manual, APC UPS have that kind (usually long-term pressing ON/OFF, but this differs from vendor to Vendor)
In Any Case, Check the Warranty of your Device, Claim a Case and replace it.
Remind - NEVER unplug a running UPS, this may lead not only to take damage to itself and can and will (already seen in the past) kill and terminate any Connected Devices to it.
By the way, to explain it with a bit of physics, due to the load on your UPS the current which is flowing, is towing a lighting to the other pole which then Shorten your Circuit and BANG your Electronics :-( (my English sucks to describe that in full perfect English)
With Regards
Electrician and IT Administrator in one Person :-)
i hope i could help ya :-)
p.s.: I Could only find The Install and User Manual
