Lost Explorer.exe

I am a comcast subscriber and with that comes Norton;  Last night I ran the complete computer tune up and had checked the shutdown computer when finished.  Now my computer will only boot up to wallpaper, I have done a bit of researching and it seems as if 'explorer.exe' was either moved or deleted during the 'tune-up'.  I was able to get to the internet, I have tried a system restore without any success and it will not boot up in safe-mode either.

 

Any help would be appreciated.

 

Joe