Intruder 800

Can anyone help plz.......I have a RX300 53 plate I have a problem with my radio. I have some times loss of sound when I first get in the car radio works with sound if I turn the key off then turn it on again I loose all sound also try change the c.d over I loose sound comes up with error 4 if I leave it for a little while go away from the car come back then put in then it's ok, but if I try any of the controls I loose sound again, any advise plz I'm in Essex