USB Device not Recognised

I have ap problem of connecting my arduino DIECIMILA Board for which I get windows error It has either nonfunctional or windows cant recognize it. But today morning I was using it, It was working well. WHAT SHOULD I DO??????????????

Hi!

I'm new to the forum and just had the same thing happen to me!
When I got my UNO R3 it worked well for 2 days- I was able to upload and download several of the demo programs. Then I tried to modify the Blink program, uploaded it to the board and now the board is no longer recognized. A different sound is made when it starts up. The board is still able to accept new programs and works but is not recognized as a USB device.
I also think the "on"led is brighter!?!?

Any suggestions please?