Is your WiFi secured? If secured with WEP, change the security to WPA and select a strong passphrase. If not secure, change it to WPA and select a strong passphrase. If already WPA, change the passphrase to a strong one that is difficult to guess.
Also, go into your router web interface and disable remote access/monitoring, and change the admin password.
Finally, what is the make/model of your router/wifi-access-point?
It is secured by WPA2-Personal totally random password.
I can't get in router web interface because I need password for it. And I'm teenager that lives with mother, and she claims there was no password. The user input is automaticly filled with Admin and I tried root, toor, admin, r00t, t00r, pwd, pass etc. .
Read the documentation for the router. You may be able to reset it to factory settings by pressing a recessed button for some period of time, then you can get in with default settings (possibly no password at all) and then reconfigure it to suit. You still didn't answer the question as to what is the make/model of the device. If I know that, I can help you better.
WPA-Personal is decent security, but the problem may be the remote admin capabilities most of these devices provide. That is a back door more and more frequently used by hackers to get access to your personal network. Once they have admin access to the router, then they can easily find out what the WPA password/passphrase may be, AND they can change the admin password so you can't get in to reconfigure the router, sigh... :-(
So, once you know how to do a factory hardware reset, disconnect it from the internet, reset to factory settings, login from your local machine (while connected via wired ethernet, not WiFi), and reconfigure the router to
Disable remote administration services.
Change admin password.
Change the SSID and make it "invisible".
Reset the WPA passphrase to something only you and your family may know.
After all this, reconnect to the internet, connect via WiFi, and verify that you can get to stuff like google.com, et al. Once that is working, reset other home WiFi devices (laptops, phones, tablets, etc) to access the new SSID with the new passphrase.
Yes, this is all a major PITA, but it is the ONLY way to secure your home network in a reasonable manner.
Well, from what I can find, this seems to be a european router - most of the links I found in a Google search were in Dutch or were from South Africa. If you are in the USA or UK or Europe, try purchasing a different router/Wifi-AP. They aren't too expensive these days.