sagem 673201t?

my box was working fine. Today it powered up showed initialising and the dots, then froze. I have tried putting it on and off standby and unplugged it and left it then switched on no different. I bougtht it from comet before they closed and have extendd warranty which is still valid, but because comet is finished I cant find out who the warranty is with. Any ideas how I can repair myself as Im sure it is just stuck