I have a Toshiba 50l711u18 that is about 3 years old. The screen has gone blank but sound still comes through. When plugged in the standby light comes on and when I try to power it up the light blinks 6 times then immediately goes black with no standby light.
I've done the unplug it for a minute (24hrs) fix with no change
For a 50" TV, the cost to buy parts to try to fix it is not really worth it, I would just buy a new or used replacement set. If you don't want to do that, start with checking over the system boards for damaged capacitors that should be easy to spot. If nothing is obvious get a power board and try that. If that fails try a new system board. If that fails, replace it.