After installing the AMD Catalyst driver which I downloaded from the AMD website, it asked me to reboot and after that I got a black screen with "Input not supported".
I know it's the graphics problem, also the grub menu recovery mode didn't help. I want the 1366×768 resolution. I'm absolutely new to Ubuntu, and this is very frustrating.
Open a text-only virtual console by using the keyboard shortcut Ctrl+Alt+F3.
At the login: prompt type your username and press Enter.
At the Password: prompt type your user password and press Enter.
Now you are logged in to a text-only console, and you can run terminal commands from the console. Then run this command and comment about the results: cd /usr/share/ati/ && ls. The command will tell you if there is a file called fglrx-uninstall.sh in the /usr/share/ati/ directory. To reboot the system from the console run the command: sudo shutdown -r now. Press the keyboard shortcut Ctrl+Alt+F7 to exit from the virtual console. In Ubuntu 17.10 and later press the keyboard shortcut Ctrl+Alt+F2 to exit from the virtual console.
If there is an fglrx-uninstall.sh file, you can uninstall the AMD Catalyst driver and reboot by running: sudo sh /usr/share/ati/fglrx-uninstall.sh && sudo reboot. After you reboot, your computer will be using the open source graphics driver as it did before.
You can use the terminal program xrandr to create a custom resolution (in your case you want the native resolution of your monitor - 1366×768 pixels) by following the instructions in this link: How to set the monitor to its native resolution which is not listed in the resolutions list?.
