I have a VHF650 made by Uniden for West Marine. It has worked great for 4 years and recently stopped receiving signal. The unit powers up, speaker works (beeps when changing settings). It seems to transmit but not receive. The unit is in a T-top box and is like new, no corrosion what so ever. Turning the squelch knob all the way in either direction doesn't create the static like it used to.

I did have my antenna mount loosen up and the antenna fell off the T-top and was hanging by the antenna wire for the rest of a trip. It didn't seem to take that much of a beating...

Is there any way to test wether it's the antenna or the radio without buying a new one or the other? Any suggestions?

I doubt it is the att. you should be able to stick a piece of wire in to here something!
Maybe the speaker blew? Try a ext speaker and try that.