No volume from radio
 

I purchased a 1999 Volvo S80 last year and love it and have not had any problems until now. I was driving with the radio on and all of a sudden the sound stopped comming from the speakers. Didn't make any noises before to indicate a problem, just stopped working. I searched the forums and it seems that there is an amp under the passenger seat. How would I go about checking to see if it is powered and working. The radio turns on, lights up and you can change channels, just no sound. Does that sound like an amp issue? Any help would be appreciated. Have to go on a long trip next week and would really not enjoy silence for 500mi. Thanks