Using a tool like the RT809H or RT809F programmer, you wipe the flash chip and write a known good dump file (the .rar you download).
The TV turns on, shows the "Samsung" logo, and then immediately restarts. Download dump samsung ua40h4200ar rar
Sometimes the issue is not the firmware but the backlight inverter circuit acting up, forcing a protect mode that looks like a firmware crash. Important Steps After Flashing Using a tool like the RT809H or RT809F
Before flashing, always back up your original, corrupted firmware. Interesting Technical Insight: Why the Dump Fails UA40H4200AR shows the "Samsung" logo
If you can tell me the (printed on the board, e.g., BN41-XXXXX) and the symptoms the TV is showing, I can help you find a more specific dump file.