I've had my Denon 5.1 surround sound system for a good few months now and i've just noticed that one of my speakers (front right) isn't working. Is this common? Ideas? Is it worth getting somebody out for one speaker? Doesn't make a massive difference but it is annoying when I paid nearly 300 quid for the system just a few months ago.

First thing I would check is the speaker wire, then all connections and settings, if all seems OK I'd see about getting it fixed under the warranty as it's only a few months old.

Quickest way is to swap the connections over with the other front speaker at the amplifier. If the speaker still doesn't work, it's the speaker or cable. If it then works, it's probably the amplifier.