Do you mean that you can't open a command prompt, or you can't open it as administrator?
If the former, can you open it directly from C:\Windows\System32 rather than from the shortcut?
If the latter, can you check the state of the Application Information Service (run services.msc)? It should be set to manual, not be disabled. Here's the description of the service:
Facilitates the running of interactive applications with additional administrative privileges. If this service is stopped, users will be unable to launch applications with the additional administrative privileges they may require to perform desired user tasks.
What version of Windows are you running?
SD