Hey there, welcome to Talkbass!
If you're playing an active bass, you should be aware that the preamp generally runs on a 9-volt battery. If your bass doesn't seem to be working in active mode, it's the first thing you should check. Generally, there will be a small battery door that you can locate on the back of the bass; it may be a plastic hatch that you can open or it may require you to remove a cover with a screwdriver.
Try replacing the battery with a fresh one and let us know if it solves your problem! In order to get the most life out of your battery, make sure that you unplug the bass when you're not using it (as leaving the guitar cable plugged in will drain the battery even if the amp is off).