Monitor doesn't turn on when UPS is working on its batteries

[Xmancode]

Hello, i have Asus pg278q (144 Hz) monitor. and i have " UPS Hantol 3000VA w/AVR, LCD, RFI Filter, Surge Protection, USB, Tel. prot. HU300 ". The problem is, when UPS is operating on its battery ( when it doesn't draw power from wall socket) My monitor turns off and it doesn't turn on.
I disconnected everything from UPS, and only Monitor was connected to it, and it still doesn't turn on (when UPS works only on its batteries). Monitor turns on when UPS is drawing power from wall socket though.

When i first bought this UPS, that is like 5 months ago, when UPS was working only on its batteries, it was able to power the monitor and the PC, and it had power for like 30 min.

Anyone have more experience about this? what you think is the solution to my problem?

 

[WyomingKnott]

A low-odds approach: Many UPSs have outlets that are on UPS power and outlets that are merely surge-protected and do not get power when the UPS is on battery. Is it possible that you re-plugged cords and the monitor is now on an outlet that is not live when the unit is on battery?

 

[Xmancode]

The UPS i am using, has 4 outlets, one says "for printer only" ( i don't plug anything on this outlet) and 3 others. Usually i plug PC to one outlet, monitor to another. So i tried disconnecting UPS from wall socket ( it is working only on its batteries) and the PC was working fine ( PC was connected to the UPS which as i said only works on batteries, and monitor was connected to wall socket).

Then i connected monitor to UPS, which was producing power only from its batteries, and i disconnected PC from the UPS ( this time only monitor was plugged in UPS). In this scenario monitor was not turning on. I tried plugging the Monitor to all 3 outlets, but same result.