All speakers not working?

Hi,

I have just replaced my cabasse head unit with a new alpine one, and now none of the speakers work? I have tried putting the standard unit back in and still none of the speakers work? All worked fine beforehand. Both units light up and play music as normal, just no sound comes out.

I have also replaced all speakers with new alpine ones and this has not fixed the issue.

I am at a bit of a loss as to where to go from here.

Any help would be appreciated.

Thanks.
 
I thought fuse as well, but I have just checked the radio fuse under the steering wheel and its fine. Are there any other fuses I should be checking? Do speakers have a separate fuse? Thanks.