I have just received an Arduino Uno Starter Kit. I'm at the point of connecting the device to my computer using the included USB cable.
The first time I connected it the following things happened:
The power light turned on. For a moment the RX and TX lights blinked. Then both stopped and all lights turned off.
The second time the power light came on, and then all of the lights turned off.
Since then the power light comes on and then the L light blinks orange in a consistent, slow pattern.
At no time did my system make a noise acknowledging the connection. I tried ports that are known to be good including plugging it into the same port that previously had my mouse.
I downloaded the drivers linked here: https://www.arduino.cc/en/Guide. It didn't seem to have any real troubleshooting advice, but I did install the USB driver.
I went to https://support.arduino.cc/hc/en-us and searched a variety of questions. None of them seemed to describe this problem at all and nothing I did from them has caused any different behavior.
I presume the blinking light is some sort of error code, but I've not been able to find any documentation explaining what they mean.