TV turning on and off after I plugged mi box s

Ever since I plugged my Mi box s to the TV, it has been turning on & off .. Ive since removed it

I've tried switching the plug off for whole day

Factory reset

I've tried updating but there's no update available

I turned it off from accessing the WiFi

Still nothing

… At times I'd be able to watch the TV for 30min now I barely can make 2min

How can I fix this please ?

Model no : LEDN50K610X3DS

exactly 7 years old