pls help - no sounds come out from minotors coect to Main-out on Presonus studio project

My presonus firestudio project used to have sounds come out to the monitors ( coect to main-out ).

It is not coming out any more.

WHen I tu on the main volume up in the fron of my machine, I heard busing noises - but there is no sound.

When I coect to Albeton 9 live, have my guitar coect to Mic/Inst 1 --- coect my PC head-phone to my stereo, I am able to haer my guitar sound

Please help me