I stoped to use my arduino UNO , for like 3 weeks.
Today I received new components, and when I tried to plug the arduino into my PC I noticed that he doesnt read the ports.
I disconected and conected again and then I noticed that the L light above pin 13 and the ON light just turn on and then they go down and the arduino turns off.
What am I suposed to do?
EDIT1 # After waiting 20 minutes I pluged the arduino to the pc again , and he was on for like 1 min but then turned off and when I conected again it does the same thing i said first.
The LED next to digital pin 13 marked with the "L" is simply an LED indicator output of pin 13 itself. So I don't believe it has anything to do with that. However, most of the time when a board acts the way your describing, it almost always is an overheating issue as Nut_NY stated and the board shutdown to prevent damage to the micro-processor chip. If you have something like an air conditioner that you can direct at the board when you plug it in to see if it stays on longer then you most likely do have a overheat condition occurring. Also make sure to check ICSP (In-Circuit Serial Programmer) pins(6) to make sure you do not have a jumper connected two pins that should not be connected.
This website below will show the layout of the board to help you along.
http://arduinoarts.com/2011/08/the-arduino-uno-anatomy/arduino-callouts1/