YUN USB Port wont work, but works with UNO

I was working with YUN from quite some time. one day the YUN stopped showing the USB port or the com port. i was working on the 'yun relayr'. I tried with UNO, the port works fine.

I tried to reset the 32U4 by pressing the reset button twice, at that time the com port is detected for few seconds and then its not seen. Now if i click the wifi symbol on my laptop i see 'LININO90a2daf31aad'.

I know that yun board is fine but its not working. i have no idea of whats happening.

Please help, thanks in advance