When you attempt to run CMD.exe or a batch file, you may receive the message "The command prompt has been disabled by your administrator". This is caused by restrictions placed in Registry. DisableCMD value is set to 1 or via Group Policy. To enable Task Manager, try any of these methods:
Method 1: Using the console registry tool
Click Start, Run and type this command exactly as given below: (better - Copy and paste)
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-pane, 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.