1. Start Windows in Safe Mode. Reboot the computer and begin tapping the 'F8' key until the 'Windows Advanced Options' menu appears. Select 'Safe Mode No Networking' and press 'Enter.'
2. Run any antivirus software you have installed on your computer, followed by antispyware software. Ideally, you should have at least two antispyware programs, as some malicious items are detected by some products but not others.

3. Delete any viruses or spyware your software detected. Reboot. If the error messages disappear, you do not need to proceed further.
4. If the rundll32.exe problem persists, your Windows rundll32.exe file is corrupt. You must perform a Windows Repair Installation.
5. Repair Windows. Reboot the computer with the Windows CD in the CD drive. When prompted, press any key on the keyboard to boot from the CD.
6. Wait for the 'Welcome to Setup' screen, which contains a list of options. Press 'Enter' to select 'Setup Windows XP.' Do not press 'R.'
7. Select the Windows installation you want to repair from the list (C:\WINDOWS 'Microsoft Windows ...'). Press 'R' to enter repair mode and 'F8' to accept the Microsoft licensing agreement.
8. Windows will reinstall the operating system, including the corrupt rundll32.exe file. Your data and other files will not be affected.