|MUI file extensions contains resources used by Windows 2000/XP MultiLanguage Version; allows the Windows interface to be changed to different languages; additional language packs can be installed using the Muisetup.exe application.|
Most MUI files are stored in the "%SystemRoot%\Mui\Fallback\LangID\*.mui " directory, but some may also be linked to specific programs, i.e. "Notepad.exe.mui." or in your case "iexplore.exe.mui
Files in prefetch are stored to help speed up loading of specific web pages or explorer pages. These files can be deleted safely. The prefetch folder should remain in-tack though
When something is causing the cpu to run at 100% then the file itself is corrupted or it is contaminated by spyware/malware/virus...or the cache files could be overloaded as well. clean your computer.
Search for ATFcleaner ... a simple to use file cleaner that will clear the cache and temps and prefetch files all in one swoop!