Hi - I had a similar problem to yours. After talking to tech support, I found out that I had to uninstall both iTunes and Quicktime, then reinstall both. After I did both, I was able to run iTunes again. Also, in a kudos to apple, I did not lose any songs I had already purchased or scanned in from cd, plus it saved all my account information. I am going to cut and paste their response to me in this post - hope it helps you too.
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Dear Vanessa,
I understand that you are a new iTunes user in addition to being an
average computer user and you are unable to open iTunes after installed
some new updates on your Dell.
First, please note that the iTunes Store team answers non-technical
questions via email about billing, customer accounts, downloading iTunes
Store selections, and the selections available on the Store.
I would like to recommend that you completely uninstall the iTunes and
Quicktime applications from your computer then reinstall both of these
applications.
If after follow these easy step-by-step articles, you still can not
open iTunes successfully, please contact either Apple technical support or
Dell support as they will be able to better assist you.
To uninstall these applications from your computer please follow the
instructions in the following articles:
iTunes:
http://docs.info.apple.com/article.html?artnum=93698
Quicktime:
http://docs.info.apple.com/article.html?artnum=60342
Note: Please uninstall the iTunes application before uninstalling the
Quicktime application.
After you have successfully removed these applications from your
computer please download and install the Quicktime and iTunes applications.
To download these applications please visit the following websites:
Quicktime:
http://www.apple.com/quicktime/player/win.html
iTunes:
http://www.apple.com/itunes/download/
Note: Please install the Quicktime application before installing the
iTunes application.
If you have any difficulties installing this software, please review
the following article:
Trouble installing iTunes or QuickTime software in Windows
http://docs.info.apple.com/article.html?artnum=93976
For more in-depth assistance, please call Apple technical support at
800-APL-CARE (800-275-2273). Help is available seven days a week from
8:00 a.m. to 8:00 p.m. central time. There may be a fee associated with
the call.
Sincerely,
Sheila
iTunes Store Customer Support
http://www.apple.com/support/itunes/ww