Hi,
Thank you for contacting Microsoft Community forums.
It looks like you are unable to install later versions of .NET Framework and it says the version is already installed.
Let’s analyze and identify the cause of the issue. It would be grateful if you could answer few questions to narrow down the issue.
1. Which exactly are you referring when you say ‘download replacements’?
2. Do you get any error code/messages?
3. What happens when you try to remove or uninstall the .NET Framework updates?
4. Do you face any issues regarding Internet Explorer?
I would suggest you to follow this article and perform the steps mentioned under the section “Repair the .NET Framework” for Windows XP.
Error codes “0x80070643” or “0x643” occur when you install the .NET Framework updates
http://support.microsoft.com/kb/976982#method2
We need to completely uninstall the corrupted versions of .NET Framework and then reinstall the required components.
You may download and install the following components after completely uninstalling using Aaron stebner’s tool. Extracted from the above article.
.NET Framework 1.1
Microsoft .NET Framework Version 1.1 Redistributable Package
(http://www.microsoft.com/downloads/details.aspx?FamilyID=262d25e3-f589-4842-8157-034d1e7cf3a3)
.NET Framework 1.1 Service Pack 1 (SP1)
Microsoft .NET Framework 1.1 Service Pack 1
(http://www.microsoft.com/downloads/details.aspx?familyid=A8F5654F-088E-40B2-BBDB-A83353618B38)
.NET Framework 3.5 SP1 (this will also install the .NET Framework 2.0 SP2 and the .NET Framework 3.0 SP2)
Microsoft .NET Framework 3.5 Service Pack 1
Hope this information helps. Do get back to us if you have more queries regarding the issue.