This is caused by restrictions placed in Registry. Disable CMD value is set to 1 or via Group Policy.
Method 1 : Click Start -> Run and type the command below :-
REG add HKCU\Software\Policies\Microsoft\Windows\System /v DisableCMD /t REG_DWORD /D 0 /f
Method 2 : Edit the registry directly
Open Registry Editor (regedit.exe) and navigate to:
In the right-panel, double-click DisableCMD and set it's data to 0
Method 3 : Using Group Policy Editor in Windows XP Professional.
Click Start -> Run
Type gpedit.msc and click OK
Navigate to User Configuration -> Administrative Templates -> System
Double click the 'Prevent access to the command prompt'
You can then disable or set the policy to Not Configured. Disabling or setting this policy to Not Configured should solve the problem.