Search:

I am sure you will find a solution, and most likely it is the mosfet.

And I have printed many 3d Models in PLA without having the heated bed on.

or you could use an external Digital high...

You should also check to see if the that the bed wires are not shorted between the controller connector bed pins. Have seen the wires touching outside of the connector before.
(If this is a new 3D...

Start with disconnecting the hotbed see if that changes anything, most likely you fried your hotbed mosfet.
This is an easy fix if you know how to solder on circuit boards. And this is the reason I...