How to Replace the Rundll.exe

1. Reboot your computer, or turn it on if it was turned off.
2. Boot into your computer's repair utility. That utility can reinstall or repair Windows from a copy of all system files stored on a hidden hard disk partition. The specific way of performing this step depends on the brand and model of your computer. For example, for recent HP computers, press 'F11' rapidly many times as soon as you see the blue HP boot screen appear. This will make the computer boot into the Recovery Manager.
3. Instruct the repair utility to repair your existing installation of Windows. The repair utility will make sure that all required DLLs are present and undamaged, and that a working version of Rundll.exe is stored in the right location. For example, on a recent HP computer, answer 'No' to the prompt about Microsoft System Restore, then select 'Repair'. After verifying the integrity of all essential system files, and resetting some Windows parameters to their default values, the computer will reboot into a repaired installation of Windows.