hi all. i just made this account to post this message. 5 minutes ago i had the same problem with .NET on win7. i was trying to install Google chrome and windows gave me the same message about needing .net 3.5 sp1. long story short...
- go to control panel,
-look for Programs and features and open it, then on the left you will see turn on/off program features...
-press that and a window appeares. search for microsoft .net framework 3.5.1; it should be there (in my list it didn't have a plus sign with 2 other options - just ms .net framework).
- by default the box is checked. just uncheck it - do not try to check it back(did that because i thought i have to and gave me the same error - could not start all features....).
- after that restart - mine didn't ask for one but that's how i work. after this Chrome installed with no errors.
seems a lot more fast and clean than to uninstall, download, reinstall frameworks... or xp virtual machines. hope this helps you - and wasn't just a "one type situation fix"