Thread can be closed. I fixed it. Thanks a lot Mootilda for your support, I really appreciate it.
Here's how I fixed it for those who might run into the same problem.
1. Download .net framework cleanup tool by Aaron Stebner
2. Open it and allow it to remove all the version of .net from your PC.
3. Now, install a fresh copy of .net. If you get an error 25015 about 'Assembly' not found (like I did), disable your anti-virus and try again but if the error persists, go to my computer > WINDOWS and look for a folder named assembly. Rename it to something like assembly_
4. Retry the installation again and it will automatically create a new assembly folder.
5. Try to run Clean Installer or other .net based program and see if it works. For me, it didn't. I got the error that I posted above. So after brainstorming for a while, I decided to uninstall .net again and reinstall it just to see if I'll encounter the same assembly error again. And voila! No error and the application ran perfectly. But do not touch the assembly folder during the second time around.
I am having problems with this too, except when I tried to download the newest version, it says I have an older version already installed. When I try to search for it, it does not appear anywhere. How can I go about fixing this please?