Protect light comes on, no power

i had a 4 channel amp hooked up in my car. it is an infinity 7540a. i installed it in my new car and everytime i connect the power it flashes the protect light once and then goes dead. i ran the bat + from the fuse box and grounded it properly. do i need to have speakers hooked up for it to work? or inputs? i havent tried hooking anything else up yet, just the power and ground. any ideas? thanks