hi.. I have an acer 23" LCD monitor. When the computer switches to UPS power, (for eg if I turn of the power from the wall socket) i hear a moderately soft buzzing noise comming from the monitor. What could the cause of this noise be?
The noise is there even when the monitor is in standby mode.

(I'm running the screen at very low brightness and contrast if it's relevant.)

The buzzing normally changes if you change brightness/contrast. It should reduce buzz if brightness is turned up.

I'll make an informed guess here.

I think it's coincidence - you're running on low brightness so there's a buzz.

But I can't ignore the UPS point. I'd bet that the UPS (maybe a cheaper one?), without proper mains synchronisation (50Hz in the UK, 60Hz in N. America) the UPS A/C output is not perfectly sinusoidal which can induce the buzz via the input mains component. I would expect the buzz to disappear if you turn up the power demand via the brightness control, but that depends on the monitor's design.

you seem to keep answering all my threads... thanks.
the buzzing doesn't go away with high brightness settings... Can it damage my monitor?

No it won't damage anything if my diagnosis is correct - i.e. on battery driven UPS only. It means that the sinusoidal interference or drift is causing an electrical resonance that comes out in a buzz.

Outside chance it'll go away if you separate mains and video cable - no overlay. I've seen that before on CRT monitors.

And you can confirm that it goes away when your UPS is mains connected? Yes? If not then you do need to contact your seller because something would be wrong.

yeah... When the UPS is connected to the mains the buzzing does go away.

Please mark this thread as SOLVED. By the way, what make/model is your UPS? It's a matter of interest to know which UPS brands have imperfect sinusoidal output.

my laptop is pledging for the instalation of a HI speed USB host controller......wat shud I do?

Please start your own thread and provide full details of what is happening.

I realise that English is not your first language but what you have asked unfortunately doesn't make sense.

What are the circumstances?
What messages do you receive?
What laptop?
What Winodws version?
What needs a high speed USB controller?
Is your laptop broken and a USB controller has failed?

Full information please in your own new thread.

It's a prolink UPS... I don't know if it's right to but a black mark on the whole brand. This IS a low end UPS so maybe it's just this model.