1. Click 'Ctrl Alt Delete' on your computer's keyboard to open the Task Manager window. Click the 'Processes' tab and search for a rundll32.exe program. If one is running and appears to be accessing a lot of your system's resources, click 'End Process' as it is likely a malicious program and not a true Windows program.
2. Run software to seek out, detain and remove viruses, malware, spyware and adware. Often these malicious programs corrupt DLL files or cause them to be deleted or moved and, as mentioned, some rundll32.exe programs may in fact be viruses on your system.

3. Reboot your computer to update any changes you may have made recently to your files and programs. Many programs and applications require a reboot for successful installation.
4. Uninstall a recently installed or changed program or application and then reinstall it using the default settings. An installed program may not have loaded properly, an installation via the Internet may have been interrupted enough to create errors or the program may have a bug. If you uninstalled a program and see a rundll32.exe error, reinstall the program and then uninstall once more.
5. Retain the services of a Microsoft certified technician, if all else fails, to review and fix your system's Registry.