Thanks for the explanation blackbird71.
I have already uninstalled CCleaner and I don't know if it created (or kept a copy after uninstall) a backup of the registry.
I am currently writing this using Opera 20 in "Windows Safe Mode with Networking".
It runs OK in Safe Mode. Something in Normal mode prevents it from running.
I have tried running in Compatible Modes, like Win7 without SPs, XP sp3, in 640x480 mode, 256 colors... and the other options in the Comp Mode menu.
I also tried repairing .NET Runtime 4.5.1 using it's own repair mode (don' know if Opera is a .NET software but I did it anyways)
And here is another hint; I installed Chrome and it also does not run! It starts up with it's GUI and does nothing, even it's setting menu does not open. (It runs OK in Windows SAFE mode just like Opera does)
(I have OPERA 12, Mozilla and IE 11 on this system and they have no issues)
This is a weird problem and I really want to fix it without re-installing Windows and see what causes the problem. I have always treated my Windows'es (3.1, XP, 7) as if they were pets and you know you don't throw away your dog and get a new puppy when he gets sick.:)
Any suggestions are appreciated.