The pot huh...
Yeah as someone has stated its probably either a loose solder connection or a bad pot. I suggest the following:
1. If its a loose solder connection unscrew the panel on the back and solder the joint back on using a soldering iron. Loose joints are normally caused by a loose knob - as in the knob isn't tightened on the scratch plate properly. So after you've sorted out the connection, try pulling the plastic knob off and tighten the nut which is under it. This needs to be done while the back cover is off as you need to tighen the nut while holding the pot.
2. If its a bad pot its probably either caused by dust between the rail inside, in which case use a aerosol cleaner thing - forgot the name for it but you can get it at electronic stores, or its a broken rail in which case you need to get a new pot. It's quite easy to solder the new pot in yourself as long as you're careful so if you're confident do it. Just make sure that you note which wire is connected to each of the 3 legs on the pot and you'll be fine!
Anyway thats it from me, hope it was useful.
Hodge