Might help us if we could learn a bit about your system. Perhaps describe your hardware from the antenna/cable/receiver/pi/power supply and connection to the internet. Do you have Graphs1090 installed? I could use a Coach - #20 by tomvdhorst
This will give us a place to start. Receiver dongles can go bad, but power supply devices often cause more problems. Do the Pi lights come on? Red steady, yellow flickering at intervals? Red says power is available though might be inadequate, yellow is generally writing to the SD card for something.
What Software are you using? A raspian os with piaware/dump1090 separately installed? Or perhaps a FlightAware image burned to the MicroSD card? This should give us a good place to start helping.
Best Wishes.