The DNS ( Domain Name System ) server is responsible to translate domain names, such as website.com to IP's such as 18.104.22.168 in order to establish a connection to that website. In many cases this process takes the most time during a page load. Fortunately, your browser will cache the result and will not ask the DNS server every time, only when trying to access new websites.
In my experience i encountered a lot of problems when using a router when the DNS requests could not be resolved. In some cases the things came back to normal after a period of time, 5-10 minutes, in other cases the only solution was to restart the router.
To avoid such problems you can use Google Public DNS instead of the automated one given by your ISP.
Google public DNS ip's are: 22.214.171.124 and 126.96.36.199 as alternate.
To change it go to network connections, right click on your active connection and press properties. In the list select TCP/IP and press Properties. In the screen that appears select to manually add DNS address and add the above IP's.
More info on setting up ip address and dns server can be found here.