While I was surfing, suddenly all programs closed off immediately and I could only see the desktop with nothing. I can now only open programs with Taskmanager, but can't open Explorer.exe. Also there is no explorer.exe in the active processes and if I try to open explorer, the icons and all come back for a moment then again go off then again and again until at last nothing comes. What's the problem? I think virus attack but avast doesn't find one.