Hello Mayank,
It seems that I had a similar issue with this router and hopefully I have a solution in the mean time. Check my post a week before yours if this was the problem.
https://supportforums.cisco.com/thread/2096643?tstart=120
My issue started once I upgraded my router's firmward to 1.01.23. What happened was that the router started up quice nicely however after a short period of time (1 to 2 hours) you would lose access to your web based user interface.
If the above is the case, reset your modem and downgrade the firmware to 1.01.19. Simply have the firmware ready and upgrade to the lower number. You might require to totally reset your modem to access your web based user interface.
I hope that this will work for you.
Kindest Regards