You need a new headunit (unless you never want to use CD's again).
You can try pulling the radio fuse for several minutes (or just disconnect the positive battery cable) and trying to see if it resets, but error 3 means the changer mechanism is jammed. VERY common issue on 2 of the 3 brands Toyota used for the headunits in these cars.
Sometimes you can take the unit apart and get your CD's out, but many times they get too damaged in the process.
You can get a replacement OEM headunit, but that will be overly expensive and it will likely just jam on you too in due time. Your best bet is to get an aftermarket headunit, mounting kit, and wiring harness. You will get a much better radio, the ability to play MP3 CD's, and usually an auxiliary input. Some also have a USB port to just plug in a flash drive with your music on it.
Toyotas in the family/next of kin:
1982 Corolla Wagon, 1989 Corolla DX, 1991 Previa LE, 1993 Previa LE,
1993 Pickup, 1994 Corolla DX, 1995 Avalon XL, 1996 Camry XLE, 1998 Avalon XL,
1998 Sienna CE, 1999 Camry XL, 2000 Camry XLE, 2002 Tundra, 2003 Tundra,
2003 ES 300, 2004 Camry XLE, 2005 Tacoma