I have SyncMaster 940nw LCD monitor, which works strangely: screen is often black(sometimes I can see unclear flickering), power indicator is double blinking one time per second. Menu doesn't show up also. I tried using another monitor - works fine. So problem is not with PC. Does anybody know what happened?

Right click on desk top and get the menu for changing screen resolution.

Most common failures in the LCD monitors are bad capacitors (bulging top/seal or leaking) in the power supply, failed inverter circuits (blown fuse, shorted transistors, shorted/open transformers), bad lamps (poor solder connections or worn out lamps). You will need to open it up and inspect the inside, see example of failed SAMSUNG monitors to get some ideas what to look for: http://s807.photobucket.com/home/budm/allalbums
Post back what you see inside so we can guide you further and it will help out other people in the future also.
http://en.wikipedia.org/wiki/Capacitor_plague

http://www.badcaps.net

More likely to have bad caps just like 203b, 205b. Please see my pictures here so you will know what to look for inside:
http://s807.photobucket.com/albums/yy352/budm/Samsung%20205BW/

http://s807.photobucket.com/home/budm/allalbums
http://en.wikipedia.org/wiki/Capacitor_plague
http://www.badcaps.net

did you try change the VGA cable? if not, try it.

I have the same problem with mine. I've kinda narrowed it down to it being the power supply in the monitor. was told it is about a $20 fix but we'll see

Sir,
You are suggested to check if you serial cable is in fine condition and it properly pluged into the Monitor and VGA. and do also try changing the serial cable .

You could have a faulty inverter or a CCFL lamp, To determine if you have a LCD screen, inverter or video card problem, read this and follow these instructions.
Defective CCFL backlight, it may have the following symptom: Screen flashs on red/pink and off. Picture stays on in red and slowly be come normal. Picture flickering with dim display or appear black. Picture flickering on and off. All these symptoms indicate that the LCD backlight lamp (CCFL Lamp) has reached the end of the life and all you need to do is replacing the CCFL lamp.
Connect an external monitor to your laptop and power the monitor up first then the laptop, if you see the normal Windows images then the video card and laptop is OK and the problem is definitely the backlight. Dim image and/or dark display on the laptop's LCD screen indicates a faulty LCD backlight and it could be the inverter that supplies high voltage to the CCFL lamp or it is the CCLF lamp is nearly burnt out or burnt out, most likely this is the case.
The inverter can be replaced easily but the CCLF lamp is more time consuming and requires soldering skills.
Check out
www.lcdparts.net
for parts, repair service and DIY info.

Sounds like you have a video card problem. If it works on someone elses PC and not yours. Replacing this video card on your PC should fix it..

Its the capacitors on the backlight power supply. Samsung installed crappy ones and they blow up after a year or two. Change out the caps and you're good to go

I wasn't able to find a 940MW. I do see a 941MW and a 940NW.
The 941MW manual has some basic instructions on page 36.

The 940NW manual can be found here.

Good luck!