If you have connected your computer to the modem using a router but your computer cannot go online, then your router (cable or WLAN router) needs a restart (reboot) so that it renews the IP address.

• Disconnect the router from the power supply for about 30 seconds
• Connect the router to the power supply again
• Wait until the flashing status of the router indicates "ready"

Reboot router vs. reset router:
Please note the difference between rebooting the router (= restarting) and resetting it: When it is reset, the router is returned to the factory settings, i.e. any configurations you may have made (such as encryption) are lost.