HD recordings are un watchable, pixelated and shadows, only started happening within the last couple of weeks with new recordings, also some older HD recordings that were fine are now un watchable with the same issues. Standard recordings are fine
If recordings that were once fine are not now, this alone would suggest an issue with your HDD - which will eventually fail. Issues with live TV would indicate signal problems, this would imply a hard disk that wants to fail - and sooner or later, likely will.
Get it reported, the chances are you're looking at a box replacement.
I am really sorry you're having problems with HD recordings.
I would love to look into this for you, but first can you confirm the following:-
Can you confirm which set top box you have?
Do you experience the same issue with live HD channels?
Does the issue happen when you watch any on demand or catch up content?
Have you been able to test an alternative HD cable?