If you actually had malware successfully install onto your system (as you've stated: "viruses"), there's a fair chance some of it still remains, even if you've used one or two removal tools. This is particularly true for multiple instances of infection. Until you are absolutely sure your computer is clean, there's a good chance you're simply chasing your tail. I've seen instances of adware re-spawning its processes in Task Manager after a few seconds delay, right after removing the more visible traces of the adware files. This stuff can embed itself in all manner of hidden places on a system and auto-regenerate from those places, particularly after restarting a system.

Of late, I've run into more and more instances of users infected by 'routine' adware that leads directly to viral infections. These infections are tougher to get rid of than the ones a year or two ago. I don't know if it's a genuine broad trend, but it sure seems like it.

the screen still shows up every time i load Opera
How? Is it a tab or it simply hijacked your start-up / start page(s) setting?

Try AdwCleaner.