iBook G4 Sound Sometimes Doesn't Work

I got a mid-2005 iBook G4 with a 1.33MHz PPC G4, 1.5GBs of RAM, 12-inch screen, and OS X Leopard. I have a problem where sometimes, the sound will work, and sometimes it won't, when I push the buttons, there is a no symbol on the sound level, and when I head into settings, it shows no output devices. I have this problem in a test user too. Could this be a hardware issue, or some glitch in OS X (I have 10.5.8).