Help, my SE s500i has stopped ringing.

Have had a Sony Ericsson s500i for about 16 months, sometimes the ring tone has seemed a bit crackly but switching it off and on usually sorted that out.

It did work earier on today, when I have an alarm set, but later I realised I was missing texts. Checked it over to make sure it wasn't on silent - it wasn't - then rang it from another phone, it's lighting up and vibrating, if I have that on, but not ringing. Hmmm!

Any suggestions?

I'm off to bed now so I'll check back tomorrow.