My Proton 320 radio has stopped working, although the clock function still works. Is this a simple fix? Where could I find a manual?

Unfortunately, Proton discontinued these a very long time ago. There is not very much information available about them. The cause for the radio malfunction could be a number of things. One possibility is the switches. There is a foam gasket around the switches that degrades over time. If pieces of it get stuck inside the on switch, or lock the off switch, it would prevent the radio from working. You could try taking it apart and use a can of compressed air to clean out the switches. I had a problem with the radio turning on all by itself and the compressed air cleaning solved it.