Control-Alt-Delete should get you to the Task Manager.
There you can see your running Applications, and you can kill whatever is hogging your system. (Or do the same in Processes.)
It sounds as though something came along via Opera and is stalling out your system.
Plus you can use File at the top left corner of Task Manager, and "New Task" gives you your Run command line, so you can do pretty much anything from there. You are posting here, so I assume you have another computer, and you can Google for any run commands you want—such as system restore.
You might want to Google about Task Manager too, because you can basically run everything you want from there.
(In the future, use the freeware NTREGOPT [NT Registry Optimizer] and its companion ERUNT, which are free and much better than System Restore. Take a bit of time to read the README textfile that comes with them.)
(Also in the future, firewalls such as ZoneAlarm include taskbar icons that let you lock off internet access automatically after, say, 10 minutes away from the computer.)
Good luck.