Computer Freezes but comes unstuck with volume

My computer keeps freezing while doing tasks such as surfing the web or typing in Pages.  Oddly enough, when I adjust the volume it unfreezes the program.  I own a March 2011 Macbook Pro.  What do you think the problem is?

Error 20, 21, 34, 37: These errors typically occur when security software interferes with the restore and update process. If you are using a PC, follow this article to resolve this issue.
Above from:
http://support.apple.com/kb/TS3694
Next I would try placing the iPod in recovery mode and then try restoring the iPod. Note that this will erase the iPod. For recovery mode see:
iPhone and iPod touch: Unable to update or restore

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