Have a look at the Wiki definition of Default Gateway.
There are many possible reasons why you are unable to connect to the Internet and the contributing factors vary for each computer.
To configure a Default Gateway
Open Network Connections
Click the local area connection you want to configure, and then, under Network Tasks, click Change settings of this connection
On the General tab, in This connection uses the following items, click Internet Protocol (TCP/IP)
, and then click Properties
On the Alternate Configuration tab, click User configured
. Type the values for the IP address
, Subnet mask
, and Default gateway
If you currently have TCP/IP configured to obtain an IP address automatically, you must manually configure a TCP/IP address and subnet mask in order to configure a default gateway.
Open the Command Prompt and type ipconfig /all
then press enter.
These are the values you will be using for the user configured IP address, Subnet mask and Default gateway.
See if there is anything in this Micro$oft Article helps: Page Cannot be Displayed