Buttons are registering intermittently?
If you find you are having to press hard to register an input I would recommend ensuring the board is not offset and cleaning all the buttons contacts and membranes with isopropyl alcohol. Sometimes a little more than a rub with alcohol may be needed. I prefer the lightly rub the area with scotch brite prior to cleaning.
I have prepared a short video
showing how much difference a proper clean can make.
My device will not power on with batteries
Please ensure the battery polarity is correct. Not all battery connectors are the same. Double check the ensure the red battery wire is going to the + pin on the Power Board.
No display when using HDMI out
Your TV / Monitor may not be able to display the low default resolution if using an older pre-configured image. You can edit the boot/config.txt and increase the default resolution or try using the newest base image available through the Downloads area of the website.