Uninstall Opera (keep your data if you want). Then, download the offline installer from https://www.opera.com/download, launch the installer, click "options", set things how you like and install. If that doesn't work, you can rename your Opera profile folder if you want so Opera creates a new one. If that doesn't help, you can put the old one back.
If that doesn't fix it, run through these steps to check your system files.