Heads up display not working

[Green Guy]

Hi

I have a Toyota prius 2011 gen3 T spirit.

Heads up display started to flicker between bright and dull light display a few times and then just went off. Now it doesn't work.

Just wondered if anybody else as had the same experience. and where the problem could be. 

Could it be the HUD unit under the dash? Which looks like it could be a difficult job!

Thanks in advance.

[Green Guy]

I was thinking, because it was flickering between bright and dim before it went off. Could it be something to do with the toggle dimmer switch for the heads up display. (variable resistor maybe)

Just trying to get a few ideas before I start pulling things apart.