I have Mediacom cable internet and their provided modem/wireless router a Cisco DPC3825. Each of the laptops experiencing the trouble have Windows 7 64-bit.
When connecting to the wireless network each computer will take a second or two to connect and then toggle from "no internet access" to "internet access" however, no websites are accessible for about five minutes after connecting. After that, there aren't any problems. It happens on all 3 of the laptops I have available and none of them have problems on any other network. It seems like my phone doesn't have the delay issue when it connects.
I've power cycled the modem/router along with a DNS flush. I have some of the DNS servers manually set to Google DNS addresses and one just default. I've contacted and had Mediacom support try all its tricks. They changed the SSID and password along with resetting the thing remotely a handful of times. It was installed just this month and seemed to pass the tech's checks upon installation. Nothing in the settings has been changed, but it's been exhibiting this problem from the get go.
This guy seems to be having the same problem, but no solution was posted. http://www.dslreports.com/forum/r27372861-IA-Connection-to-Mediacom-wireless-Modem-no-internet-
Help greatly appreciated.