tv?

lately my wife and I have had our bedroom TV turn on without the TV screen coming up, instead it shows up with a 1/2 inch or smaller line in the middle and across the TV which if we leave it as is for about 5 to 10 minutes it starts to flicker little by little and eventually it opens up to a full and very clear screen as it should look and was hoping to find someone whom may advise me as to what to check or replace in hope it works afterwards.