No C drive showing on my computer.
It is there under start button Explore

Was it there before?

Yes it's been there for long time.
But now it's gone.
All the other drives are there but not C.

Does the computer work fine otherwise?

Right click My Computer and select Manage > Disk Management
Is the drive listed there? If so, does it have a drive letter?

Drives without drive letters will not show up in My Computer.

Yes it's there.

oops Drive D is gone now too.

I think we need some more information about your computer, Windows, and history of the problem.

Have you scanned for malware?