Windows 7 losing functionalities

For about 2 weeks now, my Windows 7 - 64 bits has a strange behaviour and "loose" functionnalities !
For instance, I cannot "personnalize" the display parameters, or change the screnn resolution. I get a message like "Not supported with this interface" (My system is french and I translate the message !)
I have an ATI graphic card and can change these information through the Catalyst program
On the other end, I als found that the "Theme service" does not work and is probably not present. I cannot either start the "Window session manager"

Other problems : I cannot manage User accounbts, when I can access the UAC.
For videos, it seems Audio codecs are not recognized (I reinstalled the pack of audio+Video codecs I used and only the Video codecs are recognized

There are many other problems like these ones

I wonder if I should run an "Install-Repair" of Windows 7 ?

Please excude my english, as it is not my native lqnguage

Thanks for your help Have a good day

First check for infection by running Malwarebytes : Free anti-malware download full scan, in Safe Mode if necessary.

Then test the System files for damage using SFC /SCANNOW Command - System File Checker

If files won't repair after repeat attempts then you might consider a Repair Install

However if this is preinstalled factory Win7 or does not have a perfect install as demonstrated in Clean Reinstall - Factory OEM Windows 7 I would seriously consider deleting all partitions during a booted Custom reinstall and investing about the same amount of time getting it perfect.

Thank you
I think I'll opt for a "Repair - Install" as I would like to keep all programs and settings I've installed these last months !
Have a good day