your endstops are either not working or connected incorrectly.
Also try swapping the wires over on the fan connector.

I've often bought cheap fans and discovered the wires are reversed.
Because the sockets only fit one way people, tend to assume they are correct and something else is wrong.
Nope - the chinese have a somewhat random approach to 'standard' configurations.

Either that or you need a new fan :-)

And yep - the printrbots were really great machines.
Still no idea why the company went under - they sold as many as they could make and rarely got a bad review.