How to change the color mode on nikon d50 - Nikon D50 Digital Camera with 18-55mm Lens

You should check two switches.

First, on your lens, be sure it's set to M/MA not M. That puts the lens in auto focus mode.

On the camera there should be a switch that shows C/S/M. If switched to M, it's on manual focus. Change this to S for single auto focus or C for continuous auto focus.

I'm not sure what you mean by "multi-colour mode" but this page shows all of the possible playback display modes and describes them. Hopefully this helps you. I use a D7000 which is quite similar and I've never seen a multi-color mode. Nikon D50 SLR Review

I think if you don't have the repair manual and don't have the skills to repair electronic equipment, you won't be able to repair this camera. (I do have a D50 repair manual) Yu do have to remove to many parts to come to the switch, to look if anything has broken, or only oxidation is the problem. Better contact the Nikon repair canter and ask what it will cost you. Then decide if you want to go on with this camera or buy a new one. (if you own an AF lens without build in motor, go of a D90, D7000, D7100) If you have lenses all wit guid in motor, you can choose any Nikon you like. Cold be a cheap as 300 dollar. (NEW)

Look at your memory card. SD and SDHC cards have a slide switch along one edge. The position farthest from the metal contacts locks the card, protecting it from writes. The position nearest the contacts unlocks the card.

Set the camera's shooting mode to one of the two remote modes. Quick-response remote takes a picture as soon as you push the button on the remote. Delayed-response remote waits two seconds so you can hide the remote behind your back.

Use manual shutter speed is 80 n apptur is 5.6 ok...

Try to put PTPUSB.inf into C:\WINDOWS\inf directory

You can download it here:
http://www.infdump.com/download-inf-files_new.php/inffiles/P/PTPUSB.INF/5.1.2600.0/download.html

You can't, there is no black and white mode on the D50. You will need to take color photos and convert them with photo editing tool.

When in playback mode, press the navigation dial up or down and you'll scroll through various information screens; highlight areas, histogram, exposure (exif) data etc.

Replace the button battery 1.5 voltsX2 your auto function will work properly.