So you are happily printing… maybe you just got your Solidoodle or maybe you've successfully printed many wonderful objects… and suddenly your hot end stops being hot. You may notice this when you come back from getting a coffee and the printer is still moving, but nothing has been extruded for some time.
Sometimes the fix is as easy as ensuring that the electrical connections are solid. But, maybe you need to solder a connection back together. Here is one example of where the connection broke and solder was re-applied to fix the connection:
Lots more discussion and examples here: Hot end isn't