I let my neighbor borrow my weed trimmer. Now it will not feed line. I use to could bump it on ground and it would automatically feed line. Could he had taken trimmer end apart and lost something? All there is is a spring under trimmer head.

If He ran out of line he could have added line improperly . In which case you could try checking the line to make sure it is spooled properly.I don't know about all of them but mine does have a spring..

Should be a hand grasp knob with a nut inside it, then a spring, then the spool. The line could be wound in the wrong direction, or be binding by not being held taunt during rewinding.

I'm betting on the idea he ran out of line and did a poor job refilling the spool. Redo it yourself.