@KLP 

Forget the saved network on the laptop and reconnect. If you still get a message of no internet, assign a static IP address along with assigning DNS servers.

@KLP I faced the same issue. Spent half day to follow many advice but at last, I plug the pc directly via the Ethernet port and the wifi just can connect to the internet! Don't know why. 

@KLP I know your question was asked over a year ago, but I had this same issue today with my brand-new Deco system.  All of my devices connect without issue to the wifi except one Windows 10 laptop.  I tried lots of different things suggested by people on these sites (disabling fast routing, etc. etc. etc.) and nothing worked.

Finally I found someone who had a solution that worked perfectly for me... changing the IP address of my computer's Wireless Network Adapter (via properties accessed in the Network & Internet Settings) from being dynamically (automatically) assigned to being manually assigned.  You can get the IP range and DNS Server information from the Advanced tab in the Deco app and then just type it into the properties of the computer's adapter settings.