Arduino Uno not working

I have a problem with my Arduino Uno R3. I can upload sketches perfectly and the RX and TX LED light up as they should, but the sketch doesn't do anything. I even tried the "Blink" example with the built-in LED and nothing else connected. When the sketch doesn't involve the built-in LED, the LED is on like it should be, but if I upload a sketch involving the LED it just stays off after flashing during the reset. Can someone help me? I have been using my Uno to upload sketches to my ESP8266 wifi module, and that uses 3.3V. Would that have caused it?

Does the IDE report a successful upload?

That's really weird.

The IDE reports a completely normal upload and the RX and TX lights light up just as they normally do when I upload code.

I'm having the exact same problem, i can't upload anything but sketches that modify the state of the built in LED, I mean, I can not upload sketches that involve any pin and make them work. There are no error messages about compilation or communication.

I tried changing the Port, reinstalling the Arduino program and rebooting my computer (because this Arduino UNO has been perfectly working last year).

Today when I tried to upload a new sketch it kinda crashed, TX and RX blinked shortly and L1 kept ON, but nothing happened. The only sketch I have been able to successfully upload has been the Blink example of the built in LED, and I'm able to modify the delays, but nothing else.

All this makes me think that it could be possible that there is some kind of software trouble, because my sketch did not involve serial communication or anything harder than RGB control...