No video
Troubleshooting: no video
A black screen is alarming but usually has a simple, recoverable cause. Work through these checks in order before concluding the console is dead.
Confirm power
Look at the power LED. If it is off, the problem is the adapter, the power switch, or the internal power circuit, not the video output. Verify you are using the correct supply for your model with the right voltage and polarity.
Reseat the cartridge
A poorly seated or dirty cartridge often produces a black screen or a colored garbage screen. Power off, remove the cart, clean the contacts with isopropyl alcohol, and reinsert firmly.
Check the cable and input
Confirm the AV cable is fully seated and the display is set to the correct input. If you are using RGB, a black screen with audio present strongly suggests a sync problem, your display may not accept the console's composite sync. Try composite as a test, or add a sync stripper.
Test on a CRT
If possible, connect to a CRT via composite or RF. If a picture appears there but not on your modern setup, the console is fine and the issue lies in your cable, scaler, or display compatibility.
If the LED lights, the cartridge is clean and seated, and even composite on a CRT shows nothing, the fault is likely internal, suspect the power regulation, a failed capacitor, or the video encoder, and move toward board-level diagnosis.