before you go spending money, change the fuse in the Plug first , then open the box and look for internal fuse ( take it to somewhere like Maplins and replace that.
There is an internal fuse on the PSU. It is a vertical cylindrical device (which does not look like a fuse) close to the power socket. These are aparantly hard to obtain. I recently obtained a new PSU from Pulsat who are a main importer (talk to Roy). The issue you face is what caused the PSU / PSU fuse to fail. In my case it was one of the Sharp tuners which had burned out.