Prius 2008 base audio system not working at times

my prius 2008 I have been using for past 8 months or so was running fine with no issues until recentky its audio system stsrted malfunctioning .. the power/disc/am/scan or volume tab wont function but it can be operated through the button on steering wheel . after restarting car two tines it started working. what is the issue and how can I get it fixed . I dont to have any warranty on the car whats is the best and economical way to solve the problem. Looking for so e good advice