What is wrong with my RDR-HXD860's 'TITLE LIST'?

I had one model in use until the HDD was full. I then brought second one into use rather than make space on first machine.
Both machines were purchased at around the same time. Never had any problem before. Both very good machines.
I know I have 24(23) titles on my HDD. but am unable to see them when I use TITLE LIST.
The Blue Screen comes up, displays an empty page of ruled lines and then cuts out.
I know titles are there as I once got the list to appear correctly in full. I have even been able to delete one item, this to see if I had access.
I can get a random title to run if I use OPTION and select PLAY or PLAY BEGINNING. Thus I assume the list still exists.
This has only started in the past two weeks.
I tried using the navigation buttons as offered to a user with similar problem, without response.
The second machine has not always been in full use, it has mostly been in standby but all was well when it was occasionaly put to use, until now.
Any ideas?