Initially connect the modem directly to computer and check the internet connection is stable or not.
If it is stable, proceed with following steps.
Uninstall and reinstall the adapter and try to connect to any unsecured network, and check the internet connection is stable or not.
If it is stable with some other unsecured network,
then the problem is with the zoom router.
then change the channel on router(try eith 1,3,11 or 13) and check the connection.still same problem, Update the driver for the router to latest one.
If connetion is not stable, then the problem is with the Belkin USB adapter.Update the driver for the adapter and check.If still have a problem,Install the adapter in different computer and check whether the connection is stable or not.(This is the case router works fine,but wireless connection is not stable).If not stable in different computer, then there is problem in USB.