Hmm...this will be why then probably, since it is a very sensitive connection since it is used to pick up record deck signals.
So your amps not digital then
Well, it should be the same as the phono really...using that type of connection, 3.5mm, just like what is coming out of your laptop to connect to it which then connects to a stereo output. So just check around the back.
Another thing to try though if there are no connections is to lower the sound on the laptop, and try to increase it on the amp instead, or try the other way.
One last thing, go into Volume Controls on the taskbar on the right by double clicking it, and just check for 'Microphone' and if its not muted, mute it.
if its not there though, go to Options, Properties, and then click to show it on the volume control. Press okay, and then mute it if its not already. Does this help?
I hope this helps