Unplug the unit. Let it sit for 5 minutes (to discharge any capacitors). Open it up. Check for blown fuse(s) with a multimeter. There might be more than one.
I don't think you'll be able to install a new amp. Let alone buy one.
I can't find any info on that unit. If it was an expensive item then have it serviced by a professional if you don't find anything obvious. Otherwise throw it out and replace it. Most electronic items are not ment to be serviced / worth servicing.
Or you might have blown the output transistors.
