If you go to Command Prompt and type shutdown /?, you should see a list of commands available. If it says something along the lines of "command not recognized", you don't have it.
Go to C:\WINDOWS\System32 and look for any file called 'shutdown'
If you don't see it there...Well unfortunately I don't know what to do from there, wait for a response from another member of CH. 
The curious thing is, he says that he can type "shutdown -s" in the Run box (in the Start menu) and it does the expected thing.
On the face of it, the only explanation is that shutdown.exe is not in a folder listed in his PATH system variable. Therefore that variable has become damaged or corrupted.
A quick test for this would be to type "C:\Windows\System32\Shutdown" /? at the prompt (in any folder). If it works, the next step would be to check if C:\Windows\System32 is included in the PATH.
I would be very interested to know what happens if smlh89450 -
(1) Uses the Windows Search to find if c:\windows\system32\shutdown.exe actually exists on his computer.
(2) Opens a command prompt in the folder c:\windows\system32
(3) Issues a DIR shutdown.exe command and sees in its output that the executable is present.
(4) If it is present, types shutdown.exe /? from the same prompt while still in that folder.
(5) Types PATH at the prompt.
If the file is found, and if it shows up in a command prompt DIR, my next step would be to investigate whether the folder name c:\windows\system32 is still included, and not mangled, in his PATH system variable. I suspect this may be at the root of his problem.
The default path is
C:\Windows\System32\;C:\Windows\;C:\Windows\System32\Wbem I believe.
After all, the command prompt searches along the PATH for external commands (ie not internal to cmd.exe) and if it does not find them, returns the error described.
The fact that ipconfig.exe lives in c:\windows\system32 also is making me wonder if a mangled PATH system variable is to blame... an incautious edit could damage it.
The problem (alas, endemic in help forums) is that we may never know whether a guess was correct, since many users simply read the advice, shamefacedly realise their previous error, and never come back...
To view or change environment variables:
1. Right-click My Computer, and then click Properties.
2. Click the Advanced tab.
3. Click Environment variables.
4. Click one the following options, for either a user or a system variable:
• Click New to add a new variable name and value.
• Click an existing variable, and then click Edit to change its name or value.
• Click an existing variable, and then click Delete to remove it.
Reboot needed to see changes take effect.
