Blue screen slowly turns black with horizontal black lines

Toshiba LCD 40 inch

After switching on the the standby light turns directly to green after a few seconds but no display or sound for a while, but if i let it stay on for like half an hour or more the screen turns on but the blue screen starts slowly turning into black with horizontal black lines in a glitch type effect and then in a while turns fully black. I've changed the power cord and tried the 20 seconds off reset method but none seems to works on rare occasions the screens stays stable as in a working condition. Showed a video of this to a repair guy and he suggested a screen replacement which is too costly for me, any workaround you guys can suggest? On opening up the tv the circuits and all seemed fine without any burn marks as such. Would appreciate some insight into this! Thank you