First scan with anything and everything you got. Antivirus/spyware etc. use a registry cleaner to remove invalid paths and such.

Keep taskmanager open when accessing the folder so you can find out what process or program causes to 100% CPU usage. Try stopping the process/program to see if CPU returns to normal.

I would suggest that you make a HighjackThis log and post it at e.g Norbies world to see if someone spots something out of the ordinary.

If that doesn't help:

Do this in steps. Like in removing something then trying again if the problem persists. Make note of any error messages and access violations.

If you have an empty external, try moving the entire folder to it. In case of access violation message install Unlocker and use the shell extension option.

http://ccollomb.free.fr/unlocker/

Try removing all your codecs to see if it helps, but this is probably due to a bad download.

Then see if you can access the folder after removing them and if you can, burn the files to disk and then delete the whole folder.

If you still can't access it then delete all mediaplayers and see if that helps with access.

Post any question or new discovery in this same thread