Arduino won't talk to PC, won't flash pin 13 LED

I just got an UNO. This is my 1st time using the Arduino. I plugged in the cable and everything appeared fine. So I ran the 1st tutorial (blink). Selected the comm port and downloaded the file. All appeared well, but I couldn't tell if it was actually running since the blink appeared to be at the same rate as the default. So I changed the high time in the program to 2 seconds, and the low time to .5 second. I downloaded the program. And now the light does not flash, Windows does not recognize the board is plugged in, the comm port is no longer on the list. When I hit the reset button the led flashes rapidly and then has a faint glow that is on consistantly.

What did I do and how do I fix it?

Thanks, -Tim

Here is the code after I modified it:
void setup() {
// initialize the digital pin as an output.
// Pin 13 has an LED connected on most Arduino boards:
pinMode(13, OUTPUT);
}

void loop() {
digitalWrite(13, HIGH); // set the LED on
delay(2000); // wait for a second
digitalWrite(13, LOW); // set the LED off
delay(500); // wait for a second
}

Hmm, you might check the troubleshooting guide: http://www.arduino.cc/en/Guide/Troubleshooting#upload. Are you sure that the COM port that appeared before was really the Arduino? Try a different USB cable (make sure it's firmly connected). Does the power (green) LED on the board go on?

This doesn't explain why you have to press reset for it to work, but might explain why you are seeing what you see with the LED.

Swap your numbers 2000 and 500. Does the LED glow even dimmer? Try keeping the two numbers the same. 2000 on, 2000 off. You aren't staying off long enough to see a flash. Half a second is probably slow enough that it looks like the LED never turns off.

1/2 second is plenty of off time.
I have a colon on a time display that changes state every quarter second and that is very easy to see.

I ran through the trouble shooting guide. The board doesn't respond even after hitting the reset. Reset only cause the pin13 led to flash rapidly. But I am expecting it to go on 2 seconds off .5 second. I tried 3 different USB cables in different ports on the PC (front, back, and hub) with no joy. It programmed fine once, the second time was when I had the problem. It appeared to program fine, but never ran. The power light comes on and looks fine the led connected to 13 is the one that is on dimmly.

I get the same result when I disconnect my powered hub from Windows, esentially using the hub as a power supply. This tells me I goofed something up on the Arduino end somehow, and the PC is not the issue.

Is it possible I goofed up the bootloader somehow?

I found the problem. There was a solder ball shorting two pins on the resitor pack in front of the USB. A light technical tap cleared up the problem. I am up and running again. Thanks for the help.