Samsung tv doesn't show image, but shows text 'smart tv' when turn on

UE55MU61KXZT

Hello, i got a troubled tv, after almost 2 years it didnt see any signal from antenna and hdmi ins, after remote help from samsung they sent me technicians and changed motherboard in warranty.

After 10 months the exactly same thing happened (but this time it’s out of warranty) so yesterday they tried again connecting to it remotely but couldnt fix the problem.

Now today the tv is not showing any image, it turns on, it shows the starting text ‘Samsung Smart tv’ and then turns black, after i tried an hard reset with the power button it turned on, stayed for 20/30 seconds blue then suddenly it worked as usual, could see Netflix but just for 1 minute and then it turned black again, so i have no idea what to check