Hello, today I got an Arduino Uno R3 clone. I connected it to my PC and then the L light started blinking rapidly. When I uploaded the example "Blink" sketch L light blinked a few times(this time faster) then the sketch ran. But after the loop function ended it stoped and L light stayed on. I currently cannot upload any new sketches, the same things happen over and over again. Sorry if this is normal or something, I'm pretty new and don't really know much.
d3ds1r:
... But after the loop function ended ...
The loop function should never end as long as the controller is powered.
Arduino may be broken - did you check out some other examples?
Maybe just the bootloader is lost. You can upload the bootloader back. Here on web is a guide and also lots of discussion around it. However, you will need a programmer-HW or another Arduino.
You say you're unable to upload a sketch. Presumably you get an error. What is that error?
Does the port still show up in Tools -> Port?
Were you supplying power from an external supply when it failed? How was it connected if so? What else, if anything, was connected to the board and/or power supply?
L light stuck on and no port visible in tools -> port (when the board previously worked) is signature of hardware damage (failure of 16u2), sometimes caused by improper power supply (ie, abuse of the power rails in some way); the stuck-on LED is caused by the dual opamp used to do power supply switching, and to buffer the LED so it doesn't load pin 13, failing, as it does when power rails are abused; the result of this is generally that all pins of the opamp are nearly shorted to ground, keeping the LED on 100% of the time. The conditions which cause this sort of failure also typically take out the 16u2 used as serial adapter on genuine boards and the fancier clones, leading to the upload failures and L light stuck on appearing at the same time.