Please help me! :)

Hi - I'm not even sure if this is spyware or not. Just wanted to see if anyone had any ideas? Out of nowhere when I turned on my computer yesterday, I have one of those error messages on my computer - "Windows explorer has encountered a problem and needs to close. Etc, etc." If I click "Don't send" for the error report, everything on the screen goes blank for 2 or 3 seconds. (except the desktop wallpaper). Then everything comes back including the same error message - which is ALWAYS ON TOP!! The start button doesn't respond through mouse click or keyboard and the whole bottom bar is unresponsive. I do not want to reformat everything so I'm looking for someone very kind to help me. Thank you very much!