When I try to open a Command Prompt in Windows 7, the following message comes up:
Windows cannot find 'cmd'. Make sure you typed the name correctly, and then try again.
How can I overcome this problem?
Have you checked for/cleaned some malware recently? Sometimes malware will hijack the cmd.exe and cleaning the infection can render the cmd.exe missing/useless.
Have you tried Windows 7's in-built System Restore to restore to a point when it did work? If not perhaps you could try that.
Perhaps run Window's System File Checker to see if it can find/replace the missing cmd.exe (if it is indeed missing).
I had the same issue, solved by running Malwarebytes.
Go here install/update and run a full scan.
Copy cmd.exe from another working machine and copy it to your System32 folder. This thread has download link. But it is safe to copy it from another machine that you own.