Please help me fix this without reinstalling ((

In windows 7, i cannot uninstall or install
framework 3.5, apparently, it's pre-installed
with the os and i can't touch it

My guess is, a stupid registry cleaner got
rid of some of the 3.5 keys.

Also .. .

When i try to turn on "windows features"
in win7, i clearly see that framework 3.5.1
is unchecked .. .

But when i check it, it cannot be turned on,
& i get this error:

"An error has occured. Not all of the features
were successfully changed." All the time .. .

I don't know how to fix it, update 3.5.1
or activate it, i'm so lost

Also, i cannot reinstall win7, because i'd lose
Tones of os customizations that took me
7 months

Please guys, try to find a way to make me activate
3.5.1 in my system

Lesson: Never use registry cleaners. They "clean", they mess up, they don't help.
Don't buy into the "clean" computer nonsense.

We see cases every day here where WIn7 is ruined by Registry Cleaners, Optimizers, Game Boosters, and other tweaking outside of normal system settings.

These users haven't figured out that Win7 is already the leanest OS ever and cannot tolerate these tweaks relied upon in XP and early Vista before it was trimmed using Win7 technology.

These will almost always ruin your Win7. Period.

The only Registry Cleaner which is not a sales scam or sketchy is CCleaner's Registry tab, although some experts here will not even use it. I have used it for 10+ years on hundreds of installs representing thousands of uses and trust it completely.

When you ask us not to advise a Clean Reinstall because of "tons of Customizations" it tells me that you need to reinstall to try Win7 in its native, feather-light, instantaneous state.

Follow these steps to get a Perfect Reinstall then leave it alone for awhile to see how good Win7 is when it's not tweaked to death.

If you still need to get tweaky then save a Win7 backup image right after install and setup so at any point you can reimage with all your programs. Backup Complete Computer - Create an Image Backup

a repair install will certainly modify my registry & add obsolete entries & could reenable services & get rid of patches ((
please, if anyone has a less invading solution, help me ((

i need a way to fix 3.5.1 in win7

A Repair Install will reinstall System Files but cannot winnow out all settings that may be corrupt or problematic.

It is worth a try though, as is SFC -SCANNOW Command .

I'd first go back as far as I can with System Restore. If you have the disk space then apportion more space for System Restore so points last longer: System Protection - Change Disk Space Usage

Instead of a repair install, you might try running /sfc scannow from an elevated command prompt. You may have to run it 3 times with a reboot after each time.
This will be the least "invasive" way to fix things as far as your customizations are concerned, but it may in fact not work.

Another possibility is cleaning up all remnants of the .NET Framework 3.51 installation using a specialized tool, which should then enable you to reinstall a fresh copy (possibly right from the Add/Remove window).

Uninstall Framework .NET 3.5.1 From Windows 7

That's the exact one I linked to, except through another page. :)