HDMI Extenders come in pairs, a transmitter and a receiver!
The transmitter needs to be connected to the laptops HDMI output via HDMI cable, the category output of the transmitter should be connected to the category input of the receiver, and the HDMI output of the receiver should be connected to the projector input, more on that later!
So first things first and as a sanity check, this is what you have right?
And are you sure the transmitter and receiver are in the correct place?
They wont work in reverse, HDMI ports are either input or output, never both!
Also , transmitter receiver sets on HDMI extenders of this type are almost all proprietary and cannot be mixed between manufacturers, so are the transmitter and receiver from the same set?
The NEC NP400 does not have a HDMI input, only a DVI-I input, so a HDMI to DVI converter must be on the input of the projector, and the projector must be set to receive digital inputs, not analog, DVI-I can be used for both analog VGA and Digital.
Assuming the extenders are set up correctly, then the issue most likely lies with the projector and the DVI input setup.
Really, extenders work best when taking a signal from a HDMI output to a HDMI input.