CAN NOT INSTALL NET.Framework 4.0 PLEASE HELP!!! (I've tried everything)

Hi

I REALLY need help installing NET.Framework on my computer! This is when the Problem started:

I already had microsoft NET.Framework installed on my computer, however every time I would launch the game 'Terraria' through steam, it would prompt me to install NET. Framework again! So I looked it up online and decided I would uninstall all the versions of NET. Framework on my computer (of which there was an old version, and version 4.0) and then re-install it, to fix the problem. HOWEVER, when I went to re-install it (NET.Framework), it failed with the error code: (0x00000BC9), and told me to reboot my system to roll back changes made. So I restarted my computer and tried again, and it failed with the same message and error code. So next I used the clean-up tool for NET.Framework, followed the instructions it gave me and tried again, and of-course it failed again, then told me the tool was unable to resolve the issue and it had sent the log files to microsoft for analysis (no help whatsoever).

I have searched the web for help numerous times, but found nothing other than more people saying to reboot my system (exactly what the install window says). And I have shut-down/Restarted my computer numerous times, with no impact made.

Here are my computer's OS details:

-Windows 7 64-bit (Home Premium)

-Service Pack 1

And here is the full Installation log for NET.Framework 4.0: