i installesd a head unit in an 2000 impala, and the head unit turns on and works but theres no sound.?

Answer 1

is there a factory amp? if so you need to power it when your radio is on.

Answer 2

Many Impalas, even models without Bose radios, have a factory amplifier. If it's present, it's mounted underneath the rear deck in the trunk. You'd need to connect the amplifier's turn-on wire behind the radio to your new head unit's remote output. The factory turn-on wire is usually either pink or green in a Chevy, and if you used an adapter harness, it might match up to the blue "power antenna" wire.