We have had our box since May 2013 and in that time it has had a few brain-farts which were easily resolved by removing the power for a bit and reapplying.
However, in the last few days it barely works for 30 seconds before freezing - often with the sound continuing with varying quality behind a frozen picture (sometimes with green pixelation).
You seem to have to remove the power twice (after the first time, the box does sod all) before it comes back. Occasionally it will work for a few hours but I have resorted to our Apple TV to supply my son's Peppa Pig fix as it is highly unreliable.
I did manage to get into the settings the other day to see it has the latest firmware.
Would a factory reset be of any use? (I noted elsewhere that this will not impact my recordings).