monitor screen flickers

It might be caused both of them, but likely it's UPS problem as its AC-DC converter has high frequency circuits. I had similar problem when ADC converter embedded to PC went crazy once PC had been feeded through UPS. Earthing, filtering couldn't help, so i simply replaced this UPS.

Hi...It is not advisable to remove earthing. Simplest solution will be to move the UPS about 2 Meters away from the monitor. This will solve the problem.

Rgds

Sanjeev

You may also want to try some clamp-on ferrites around the power cables and VGA signal cables. Some monitors are very sensitive to noise on Pins 13 and 14 of the HD-15 connector (H-synch and V-synch) and will re-trigger the monitor. Better designed monitors will have gating circuits that "ignore" noise spikes outside the expected pulse rate and also "look" for pulses of the expected pulse width. Most EMI tends to be impulsive (relatively short pulse width with respect to VESA standards) but inexpensive monitors will just trigger on rise instead of looking for the pulse itself.