Explorer.exe causing the CPU usage to jump high and slow down your machine is not a virus and stay out of the regedit program. This problem is caused by a corrupt video file (usually) sometime audio but I have only seen that once.
This is a problem I get probably 5 times per week, I'm a tech support for Dell. Here's the fix...
First find and remember the folder you keep you video files in, the problem is usually a AVI file.
Restart you computer
Open My Computer
Open your tack manager (Ctrl-Alt-Del) go to processes Tab find and highlight explorer.exe. This should be running at almost no CPU usage
Open the folder where the video files are kept ****Important do not let your mouse pointer go into the display box until you are ready.
now let your pointer go down the list of video files one by one until you see the CPU Usage jump to a high number and stay there, usually 99%.
The file you are on when the number jumps is the one with the explorer conflict. You should delete this file, if you have to keep it you can download a conversion file to change it to some other format.
Note: Some times it may not be an AVI file but the check is the same, when the CPU jumps you have found your problem.
Sometimes the file will not delete....
Then you have to go to the Command prompt and get to that file and delete it directly.
Hope this helps. This method has always worked, it just takes time to find the corrupt file. It is possible that you have more than one corrupt file so restart after you have deleted the file and run your pointer down the list again with your Task Manager open.

Aren't computers wonderful things.... It because of all these silly little problems that I have a great job.