If you want to enable RDP on local machine, start cmd.exe as Administrator and type:
reg add "HKLM\system\currentcontrolset\control\terminal server" /v fDenyTSConnections /t REG_DWORD /d 0
… at command prompt.
If you want to enable RDP on remote machine, start cmd.exe as Administrator and type:
reg add "\\hostname\HKLM\system\currentcontrolset\control\terminal server" /v fDenyTSConnections /t REG_DWORD /d 0
… at command prompt.