1. Check the physical connection
Make sure the Ethernet cable is connected to both the router and your computer. For first troubleshooting, use cable instead of WiFi.
2. Try 192.168.0.1
Not all routers use 192.168.1.1. Another very common address is 192.168.0.1.
3. Check typing errors
Type the address in the browser address bar, exactly as http://192.168.1.1. Use numbers only.
4. Restart your router
Turn the router off, wait 30 seconds, then turn it back on and wait 2 minutes.
5. Reset the router
If it still does not work, reset the router to factory settings.
6. Find your actual gateway IP
On Windows open Command Prompt and run ipconfig. Check Default Gateway; that is your router IP.