4 track problem

Im having some troubles getting my 4-track to record with my amp plugged into it the 4-track as well. Its an AMR 64, MCR 4, real old I think, my uncle gave me it. On the right side of the 4track theres 4 jacks labeled as a whole "Moniter Mixer" and each jack itself is labeled "Input", but I am not using those, when my bass in plugged into them for some reason it wont let me record. Then on the left side theres 6 sets of [buttons for volume and equilizer stuff, switches, and a "Line" and "Insert" jack, all that for each of the 6 sets]. I am using the #1 "Line" jack to plug my bass in on the first set then my friend is also using one of the sets with a guitar in the #2 "Line" jack. We can record and it works great, but we can only hear ourselves through the stereo jack. The problem that the only way we can hear what we are both playing is if I put my amp into the Stereo jack, but then we both are played out of my amp, and theres only 1 stereo jack. Thats not good plus we each wanna use our own amp. So next to each "Line" jack is an "Insert" jack. When we plug our amps into the corresponding "Insert" jacks, we can hear ourselves. Great right? Well now when we record it again doesnt record. What I mean by it doesnt record is that the sound bars (green to yellow to red bar that shows the volume of what you are playing and if its moving you can tell its recording) arent moving at all, it just records a constant humming noise. Im not sure what to do though, any suggestions are appreciated. Thanks so much!