Cindy,

Use advanced code 244 within manuf. code 0160 to switch to DVD input on AVR-3300. You can place it on the #3 key as it should be empty. I will email you all AVR-3300 advanced codes privately.

Regarding your power on problem, when the receiver is first turned it initializes the processor. This causes several seconds of a muted condition. Please wait for this initialization to finish before entering other commands.
Also, when you hit the Tape Monitor button on the 15-1994 remote (#6 key) you effectively mute the receiver. You need to hit it again to unmute it.
Feel free to email me with any other AVR-3300 or 15-1994 questions and I'll try to help.