First of all, I want to thank you for your help.
After my last reply to your post, my computer went crazy with blue screens!!! And after several attempts to figure out what was happening, I tried several options:
1.I changed my wallpaper. it seemed to have a bug.
2.I ran a Windows Repair. It suggested me to disconnect my web cam. It seemed to cause a conflict with the RAM memory.
3.I ran a System Restore, and my Computer came back to life!
4.I could reinstall my Avast Internet Security, and it is running well until now.
Any further help will be deeply appreciated. I am very glad that AVAST Internet Security is protecting my system again.
Greetings!