Electrical/Audio problem

[tomcat]

2005 4.8iS 75,--- mi.
Hi all. Yesterday ran to Wal Mart. When I returned to the X it would start to crank, then flash a bunch of lights, click, and make a beeping sound. Sat a while to let it charge a little and still couldn't get it to start. Finally went in and bought one of those battery quick chargers. Been meaning to for a while so I figured "why not today?" Got her started fine and drove home. Today started fine, but I now have no audio except for front right and rear left speaker. Battery is less than 3 years old and amp is about 4 years old. I realize I may need to check my alternator for the starting issue, but what about the radio/amp?

Thanks,

Scott