• Delete "C:\Program Files\Opera".

• Delete "C:\Users\yourusername\AppData\Local\Programs\Opera".

• Delete all files in "C:\windows\temp".

• Delete all files in "C:\Users\yourusername\AppData\Local\Temp".

• If you don't need to save your Opera profile(s), also delete "C:\Users\yourusername\AppData\Roaming\Opera Software" and "C:\Users\yourusername\AppData\Local\Opera Software" (or the specific profile in those folders).

Open regedit and delete:

• "HKEY_CURRENT_USER\Software\Opera Software".

• "HKEY_LOCAL_MACHINE\Software\Opera Software".

• "HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\OperaStable"

• "OperaStable" in "HKEY_LOCAL_MACHINE\SOFTWARE\RegisteredApplications".

• "OperaStable" in "HKEY_CURRENT_USER\Software\RegisteredApplications".

• "HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Opera Software".

• "OperaStable in "HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\RegisteredApplications".

• Opera keys in "HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall".

• "HKEY_CURRENT_USER\Software\Classes\OperaStable".

• "HKEY_LOCAL_MACHINE\SOFTWARE\Classes\OperaStable".

• "HKEY_CLASSES_ROOT\OperaStable".

Then, download Opera from here. Launch the installer, click "options", set "install path" to "C:\Program Files\Opera", set "install for" to "All Users", pay attention to the checkboxes and adjust them how you like, and install.

If that doesn't work, create a new user account(and admin account), log into it and install Opera from there.

If that doesn't work, you'll have to investigate things outside of Opera like security software, malware and viruses. Or, you may have to uninstall that Windows update for now.