When turning on Air Window unit, APC UPS beeps shuts off. (more)

Ok, this just started a month ago. in my one room, I've had the same setup for a long time. years.

Notes:
I keep my PC on, 24/7 mostly, and its a gaming rig.. has an 850W 'gold' power supply in the PC. (never use that much wattage though).

I have a PS4, the PC, and the LED monitor connected to a NEW APC 550. (those are connected to the UPS and protection part)
the other side, non UPS, just protected, I have a tablet recharger, 500watt speakers, and a small light.

When I am just using the PC, I can turn on the Window unit A/C, with no issue. when the compressor kicks in, I hear the UPS do the click/click sometimes, but its fine. right?
If I then turn on the PS4, and the PC is on, and while playing, I kick on the A/C, it will SOMETIMES turn off the PS4 only.. I was playing battlefield 4.

Ok, so I have BF4 on the PC too, I am playing it, and do a test (PS4 off), turn A/C on, and it turns off the ENTIRE APC UPS, and I get a constant BEEP. (overload?)

The UPS battery. is full, just maxing it? or something else? as I said, same setup, this never happened. nothing else added to the entire circuit for the two rooms on the fuse).
Thing is, this JUST started happening.. I got a new APC UPS thinking that was it, because the unit was old. 4 yrs.. but if it was a overload, it would flip the breaker switch in the box in the garage...??

EVERYTHING is the same, checked all the plugs on this 'line'. breaker hosts two rooms.. just worried.. is the A/C win. unit dying? I ground things.. no extension cords from the UPS (lol).

Maybe something is failing in a component in the electronic equipment or is it the fuse in the breaker box

dying? its been in there since 1989.. (had to replace the GFDI a while ago).. (the rooms are not on a GFDI, that's the bathrooms).

This doesn't' happen every time though.. which is odd..

Any thought or suggestions would help. Worried..

Thanks
Z