Hello,
I'm using UNO R3 version. Whenever i turn off my arduino and turn on again, sketch does not start. Instead, it blinks constantly w L led. Firstly, I tried grounding RX with 10k resistor as in arduino troubleshooting, but with no effect. I've read somewhere that's because of bootloader. Is that true? I've tried several sketches, from blink to PS2 pad library example, but none of them works after turning power off and on again. Have someone had such a problem and came with solution or is it somewhere here on the forum, but my poor searching skills made me fool?
There used to be a problem along those lines. Burning the latest bootloader may help, however you need an external programmer to do that.