How to fix my hifi - No sound from speakers?

My hifi works fine other than no sound is coming out the speakers. There is no sound from earphones either, when I plug them into the earphone socket. I have tried the speakers on another system and they are working fine.

What caused the problem.....I was using the 'line-in' 2.5mm jack plug socket to plug in my mp3 player so i could listen to music on the mp3 player through the hifi speakers. When I moved the mp3-to-hifi lead, I got a load crackle noise and then no more sound from speakers.

I cant imagine its particularly difficult to fix but no-one in my area seams to do this type of work.

Its a sony HDC-MD373 mini hifi

Thanks