Sounds like the Line Output Transformer (or flyback transformer as some call it) in your monitor either has some dry joints (especially if giving it whack got it working) or it may be fried altogether...
Either way unless you know what your doing and are handy with a soldering iron, I would advise not touching it as there are LETHAL voltages involved here... best advice is find someone local who can look at it for you...
Commodore made different versions of the 1084 for sale in different parts of the world. Some had SCART sockets (Mainly UK) some had 9 PIN D Sub connectors (like the kind you have) and others had round DIN connectors just depended on which part of the world the target was for each monitor...
They all have RGB inputs and the pinouts for your 9 PIN D Sub one are as shown in this link...
http://pinouts.ru/Video/C1084dd_pinout.shtmlIf you can't make your own cable for it then you may find one on eBay or perhaps someone here may have one...
You monitor sounds like it can be repaired (difficult to tell online though) but as for converting it to stereo using the parts from each other then the answer is no I'm afraid...
