I'm using Widows XP and when I start my PC, I get an error message that says something like:
Windows can't find rundll.exe
How can I fix this?
Various Windows services will appear as or require RUNDLL and there's not going to be a singular reason for this type of problem. A corrupted program installation, or a virus after removal are just a couple examples of possibilities.
The first step to debugging this would be run in safemode and see if you still have a problem. If you do not, then there's a problem with a start-up program or service.
Go to Start->Run and enter
This will bring up a utility for limiting start-up programs. You can uncheck any or all programs under startup, and for Processes, it's a good idea to check "Hide All Microsoft Services" in order to deselect anything that isn't integral to the OS.
Also recommended is to do a full system scan with the Microsoft Malicious Software Removal tool. To do this, again under Start->Run, enter this
That'll bring up the tool so you can do a full system scan. If you do have an infection, I'd recommend backing up anything important, then reformatting.