Geeetech

That's the thing, William. If I pre-heat the nozzle, it will drip out whatever plastic was inside it. If I manually push filament through, or use the UI to advance the extruder head, then I get a dangly filament of melted PLA. But when I try to print things, I either get a small amount of filament deposited on the bed (and then, nothing); or, I get nothing.

Confused!

Hi,You may need to clean the nozzle,
You can take out the Teflon tube, heat the nozzle temperature to 200 °, and use a tool to clean the remaining consumables inside.
Specific operations can refer to this: https://www.youtube.com/watch?v=iorvvnp6Y7Y