Ok this is how you troubleshoot when you're having problems with signal flow. First of all, once you understand how the signal flows to your equipment, then you have to ask yourself "What could the problem possibly be?" For instance, this is the situation: You're using Serato, you loaded up the song, you're getting signal on your screen, on the LED lights on your screen, so that means that there is signal coming out from your laptop but for some reason you can't get it in your headphones or you can't get it througout the main system. It can either be that connection on the head shell to your tone arm needs to be clean. So if you have a cue tip and some alcohol, you can take and dip it in your alcohol and clean the back of your head shell, plug it back in to the tone arm, press play on your turn table, raise the volume on your headphone level. If you're not getting the proper signal, you're still trying to figure out what the problem is, so that didn't solve the problem. You're definitely getting volume, you're getting signal on the LED lights on your mixer but it's still not coming out clear, you're trying to figure out why. You can hear signals but it sounds real muddy. So you're still trying to figure out what's going on. Look at the cables- the cables that are connected to the mixer. Make sure everything's plugged in. As I'm checking, I'm noticing, I'm missing my left. My left input from my left turn table is not connected so that I'm only getting the right signal. Don't panic. The worst thing to do when you trying to troubleshoot is to panic. You want to just take your time and just go to the signal flow and try to figure out what the problem might be. So if I plug in the left channel, that should resolve the problem. Let's play the track. I got clear signal. So, that was the problem. That might not always be the problem but you'll experience this kind of problem when you're taking over a shift for another DJ. They might be mixing and adjusting the volume levels and EQ levels and all that stuff during their set and when you get on, they forget to turn off an effect or turn up a volume or to pretty much reset all the knobs the way when he or she first started. So you wanna make sure before you start your set, make sure you got the proper signal, make sure that everything is the right volume and the right level.