an hour ago i could play my bass conected to the interface and hear it pretty well, but i cant hear it now. I have a song in audio track 1 and i can hear it good but i cant hear the audio track 2 where my bass is 
Hi,
it’s probably a rather simple thing so please don’t be offended by these questions:
- is volume turned up on your bass (the physical instrument)
- is the gain for channel 2 turned up on your UR12
- is your bass plugged in into channel 2 on your UR12
- if you open the mixer - can you see an incoming signal?