Help My USB Device not detecting in RB751 with USB port

Hello all,
I have been using 3g dongle for my internet connection using my rb751G. I used it to do ppout for my office network, but all of sudden the 3g modem connected to the router does not come up again, that is it does not show again in /system resource/usb. Even in pppout, device is showing unknown port.

How to i restore this usb port so that I can make use of my 3g usb dongle.

Your help will be appreciated as we have not being using the router since 5days now.

Thanks
Dunga