Tried contacting Sage for help via web or by phone? You might need to have bought their support package, though still worth a try if you don't have it.
Have you been doing regular backups? If you have then you will have the data wherever you backed it up to. Depending on your version of Sage and Windows your data itself if stored in a folder called ACCDATA.
If you cannot re-install you may be able to get another disc from Sage, or depending on your version an upgrade.