USB CDC on LPC1768 problem

Hi,

I have a problem with running a USB-CDC on the LPC1768. I have a USB circuit identical to the MCB1700 board. I use the sample code for USBCDC MCB1700 board.
My program stops at the following line:
while (! USB_Configuration);
On the computer I get the message: "USB Device not Recognized."
Is it a hardware or rather a software problem? Sorry for my English.

Best Regards,
Lukas