UPS shuts down my PC with continuous beep when playing games.

UPS shuts down my PC with continuous beep when playing games.

Knowing my needs I bought a line interactive UPS with 1200VA/720W rating assuming it to be sufficient for my use. But, every time there is a power outage, UPS shuts down my PC with continuous beep while playing games. It works fine with general usage. But with intensive tasks or games, it just shuts down with a continuous beep. It doesn’t seem to sustain heavy loads.