You probably have some registry conflicts or some registry keys were not cleaned up and removed when you uninstalled the software or tried to write over it. The PC thinks its still there or there is a conflict with old registry keys so it can't install. This happens with some software. ( if you are using a MAC disregard ) The following is for PC users only:
First -- if you have not done so already, try using the Add / Remove programs utility in your Windows Control Panel. You can find step by step screenshots and instructions on how to do this at this reference site: http://uninstallmysoftware.com
If that doesn't work, or if the software does not show up at all in your control panel, then follow these steps:
Step 1 - Select and download any good software uninstaller application that has a free demo or trial version and try that first. Most of the time the free versions are enough to fix the problem - (there are some good ones listed at the link above).
Step 2 - Install and run the free software uninstaller you selected and follow its instructions carefully - you should see a screen with a listing of all the programs installed on your PC; often more programs than those normally listed in your Add / Remove control panel. Most uninstallers will find software that does not show up in your Add/Remove control panel.
Step 3 - Find the software you want to uninstall, then select and click "uninstall". All good uninstaller software will do the rest automatically. This next part is very important:
Step 4 - Sometimes you also have to clean up your computer's PC registry and remove leftover software keys and orphan files from the uninstalled software after running the uninstaller. Some of the more advanced "pro" version uninstaller programs have this feature already built into it and will do the registry cleanup and a backup automatically but some don't. If yours doesn't, then just use RegCure it usually works just as good -- you can find a free link to it on the reference site above. If your uninstaller software does have a registry cleaner built into it - be sure to use it !