Arduino Uno - Can't load code, "L" Led ALWAYS On.

Hi.

I have an Arduino Uno R3, it used to work well, but it doesn't work anymore, I can't upload code to the board because everytime I try I get this error message:

Arduino:1.8.1 (Windows 10), Tarjeta:"Arduino/Genuino Uno"

El Sketch usa 928 bytes (2%) del espacio de almacenamiento de programa. El máximo es 32256 bytes.
Las variables Globales usan 9 bytes (0%) de la memoria dinámica, dejando 2039 bytes para las variables locales. El máximo es 2048 bytes.
Ha ocurrido un error mientras se enviaba el sketch
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x3e
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0x3e
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0x3e
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0x3e
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0x3e
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0x3e
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0x3e
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0x3e
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0x3e
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x3e
Problema subiendo a la placa. Visita http://www.arduino.cc/en/Guide/Troubleshooting#upload para sugerencias.

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1 - The Operative System does recognize the Arduino board. It does.
2 - The Arduino Software does recognize the Arduino board. It does too.
3 - Any Led on the board doesn't gets on ONLY the "L" Led which is ALWAYS on.
4 - TX and RX LEDs doesn't do anything when I try to upload code to the Arduino board.
5 - Reset button doesn't do anything.
6 - I tried several ATMega Chips and it's the same... They work well when they are in other Arduino Board.

If someone could help me to fix it, if there is a way to fix it, I would be thankful.

Thanks.

Try to update Arduino USB firmware update. First check which IC on your board is responsible for USB connection. And then update the firmware

lalit90:
Try to update Arduino USB firmware update. First check which IC on your board is responsible for USB connection. And then update the firmware

This is not good advice. Many people do this just for try and then they are only in bigger problem.

So the L is not flickering at reset? If so, then there is some problem with the bootloader. It must blink 3x fast at Arduino reset (also connect USB port, or at start of programming) if the bootloader is present. Anyhow, check also behavior of Rx, Tx LEDs. Rx should blink visibly at any programming attempt.
Also check the status of the port on your PC and post the result of your observation.
And check your board if something is not hot.

L led stuck on and not blinking when you press reset that is is usually symptomatic of HARDWARE failure, not bootloader issues - namely, a blown opamp (this also takes out the power supply switching too). This is one of the two easily blown parts on Uno boards.

The fact that the same chips when removed and put into a different Uno board will work indicates that the issue is definitely a hardware problem on that Uno board. It is not repairable. Discard the board and replace.

As an aside - are those clone boards? The reason I ask is because usually on the official boards, the same things that do this will also trash the 16u2, causing it also to not detect as a USB device. The USB-serial adapter on clones often survives this sort of insult - though usually in that case, you can still upload to the board via USB, whereas you say it detects as a USB device, but gives a sync error.

It's sort of funny how the 328p is in a socket - but the two parts that are easiest to trash are both non-replaceable SMD parts.