I have these but for past many years but all of sudden they are dying in both pots

Have you fed them on a regular basis? Continuous watering would quickly wash away any nutrients in the compost. Bit early to say that it might be box blight.

It does look a bit like Box Blight, but Box has other problems too - this link has pics and names the other troubles and gives treatments if there are any https://www.rhs.org.uk/advice/profile?PID=851

Thank you for replying. Will it grow again or I should buy new one for these pots?

If you decide what's wrong with it according to the link, its worth carrying out any treatments that might be recommended, because chances are, you'll end up with the same trouble with new box plants eventually.

Thank you Bamboo.

Good new about Box that they are recovering. Thank you for the help. I fed them and water them but not too much so the feed stays in the pot.soon I will take pictures and upload them.