There are a few possible causes of this issue, including a bad cartridge, internal debris/contamination, or a hardware failure (bad printhead, bad logic board, faulty sensor, etc). Considering the drop, you likely just have a cartridge that popped out of place.
What we can try are some cleaning and reset steps.
First remove all of the ink cartridges, then clean the metal electrical contacts on the back, as well as where they mate up inside the printer, using qtips and rubbing alcohol. Dry well, then reseat the cartridges.
Then reset the machine:
unplug power at the wall outlet
wait 5 minutes
press and hold the power/on button for 60+ seconds
keep holding while plugging back in, and for another 60 seconds after, then release
Let me know the results, and I'll advise further if needed.