Find the router configuration page to navigate to in your browser. Now if you successfully got on the router settings page, try to locate firewall settings and disable the router's internal firewall. Also try to make NAT less strict, for example you can add the local IP address or MAC of your PC you're playing MTA on, to the ''DMZ zone'' (opening all ports at once) which is now a safe procedure because the main router/modem is already filtering the signal.Save the settings and reboot the router, now try again. If it still doesn't work, you can try repeating the same procedure on the main router. It might just not know how to handle traffic that is pre-processed by another router. Also, a Wifi repeater instead of using a second router can be a better idea.
If you can't see the gameplay mode of CIT, then the you must re-install your windows, I solved my problem with this solution.
Although, you can try resetting your router, use a small pin (needle or anything that is small) and find a small hole on the back of your router (maybe on the side for yours), then press, and hold it for 10-15 seconds. After doing so, wait 5 minutes and turn off your router, wait for another 5 minutes then open your router.
Sausages, try what I have replied.
maybe you're using 600x400 resolution, minimum resolution is 800x600.
is this problem really need to make me reinstall my windows? , Although I still can get into other server, the problem just occurred on CIT's server