Because of the possibility that it's an OS/update issue, there are a couple of things to try from that angle. First, if you haven't already done it, power down the computer for a couple of minutes and restart it (just in case something in the update/reboot processes has caused a glitch)... then see if the defaults are sorted out. Next, if things are still messed up, open Windows' Control Panel and select Default Programs > "Set your default programs" > Select Opera and try making it the default program.