Whenever I enable Tree Canopy Shadows the grass disapears for no reason and I can only see the outline of the grass if I focus carefully on where it was. I've tried reinstalling the game 2 times with no luck. It just keeps on happening. I have the game installed on my other HDD in the PC and it doesn't have this problem on that HDD but I don't want to use it becasue it has all my grandpa's family pictures and videos on it and I don't want to fill more data on it.

Does anyone know a solution?

This is making me mad!

I'm not sure you can get away without uninstalling that previous install. There are registry entries created when you install, and you may be seeing a conflict.

Also... Did you delete the Oblivion.ini in your Documents\games folder, when you reinstalled? If not, you should do so, letting the game create a new one, because it sounds like something is messed up and pointing back at the old install.