This is a known issue with the "hot" firmware delta. Unplug the TV, wait 1 minute, plug back in. The TV will revert to the previous firmware automatically. Then use the USB method described above.
So, what exactly is this update? Should you install it? And why are people calling it "hot"? firmware change update on sony kdl50w800c hot
It is normal for the back of the KDL-50W800C to get warm, but if the TV shuts down or displays a high-temperature warning during or after an update: This is a known issue with the "hot" firmware delta