Microsoft .NET Framework fails to install

I'm not really sure where to post this, so I'll put it here and it can be moved if necessary.

I have spent a long time recently installing and reinstalling the .NET Framework in order to play a game (Terraria), but it has never worked properly, giving me various errors. I have a log of the most recent install failure here.

Can anybody help me?

OS Version = 6.1.7601, Platform 2, Service Pack 1
OS Description = Windows 7 - x64 Home Premium Edition Service Pack 1
CommandLine = I:\248853e1b9917d70215c868228\\Setup.exe /x86 /x64
TimeZone = GMT Standard Time
Initial LCID = 1033
Using Simultaneous Download and Install mechanism
Operation: Installing
Package Name = Microsoft .NET Framework 4 Setup
Package Version = 4.0.30319
User Experience Data Collection Policy: Disabled
Number of applicable items: 11
Exe (I:\248853e1b9917d70215c868228\SetupUtility.exe) succeeded.
Exe Log File: dd_SetupUtility.txt
ServiceControl operation succeeded!
ServiceControl operation succeeded!
Exe (I:\248853e1b9917d70215c868228\Windows6.1-KB958488-v6001-x64.msu) failed with 0x240006 - (null).
Exe (I:\248853e1b9917d70215c868228\SetupUtility.exe) succeeded.
Exe Log File: dd_SetupUtility.txt
MSI (I:\248853e1b9917d70215c868228\netfx_Core_x64.msi) Installation failed. Msi Log: Microsoft .NET Framework 4 Setup_20111229_152948055-MSI_netfx_Core_x64.msi.txt
Final Result: Installation failed with error code: (0x80070643), "Fatal error during installation. " (Elapsed time: 0 00:01:10).

did you see these?

Windows 7
http://windows.microsoft.com/en-US/windows7/Windows-Update-error-80070643

If you can't repair V4 then you'll need to uninstall and reinstall it.

.NET Framework Setup Verification Tool User's Guide
http://blogs.msdn.com/b/astebner/archive/2008/10/13/8999004.aspx

Download dotnetfx_cleanup_tool.zip from the following link on the site:
http://blogs.msdn.com/cfs-file.ashx...-90-44-93/dotnetfx_5F00_cleanup_5F00_tool.zip

Downloads for Framework if required:
http://msdn.microsoft.com/en-us/netframework/aa569263.aspx

Note: Mailbag: What version of the .NET Framework is included in what version of the OS? http://blogs.msdn.com/b/astebner/ar...rk-is-included-in-what-version-of-the-os.aspx

I don't get an error code (like in that first link). It just says it encounters a fatal error.

It doesn't need to be uninstalled and reinstalled. It is already uninstalled, it just won't reinstall, whatever I try to do.