Have you tried rebooting (turning off and back on) the computer to see if this resolves it? Also, have you tried a different browser? If you get the same problem on another browser, you may not actually be connected to the internet. Even if the WiFi connects that doesn't mean there is an internet connection.
Should the reboot not help, then you may need to reboot (again turn off and back on) the modem/router to see if this is the issue.
After both of those, if there is still no internet access, then I would contact your ISP as the internet connection itself may not be working.