I already provided you the steps to manually clean up after a failed install/uninstall in another post and you seemd to have issue with following those steps. Did you finally complete all of those steps?
Regardless of which version you want to install you will have the same results until you manually clean up your corrupted install. You cannot reinstall ST8 over the top of a corrupted ST8 install.
If you followed and successfully completed all of the steps in the previous post, and it still is not allowing you to install Solid Edge, then one last one thing you can do is:
1. Open the registry.
2. Browse to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\
3. Do a Search under this location for a key containing the DisplayName "Solid Edge ST8"
4. When found delete the entire Solid Edge key (it will be a string of alphanumeric characters and dashes )