Hi Nancy,
Building onto what rave mentioned, make sure when you reinstall the product you use the correct download for your product.
I mean for CS5 products the download for Retails (Single User) product and Volume (Multiple Users) product are different.
If you have Retail product then you can download them using the link: Download CS5 products.
If you have Volume product then you can get the download using the article: http://helpx.adobe.com/x-productkb/policy-pricing/volume-licensing-site.html.
Let us know for further query.
Thanks,
Ratandeep Arora