My 340 display is off and will not allow me to change the product.

[techjoeb]

Looks like the issue is one of the start buttons. Without getting too much into the reason why, the start buttons being held down cause the unit to go into a safety mode that does not let you turn the unit on or change the product. You can isolate which one it is by disconnecting one start switch at a time and leaving it unplugged until you get the part on order. The start switch part number is 78-244S. It comes with both switches.

 

I hope this helps!

-Joe