Explorer.exe is missing from my computer

Hello,
i don't know how i can miss my explorer.exe from my computer so that i have to use task manager to do the work. i have tried to search but couldn't find it.
i also have already do sfc/scannow from command prompt but it is said could not do the requested command.

so, where can i find the explorer.exe to be download from reliable sources? or what should i do ?
need advise

big thanks
jay