Windows 7: WMC can not open the program because of a software restriction policy

I can't no longer start Windows Media Center, when I try It get out the message "can not open the program because of a software restriction policy". I have Win 7 Ultimate 64bit
It is the only program that not starts and that occurred a few days ago after installing and uninstalling some alternative such mediacenter softwares as Mediaportal and Nextpvr.
I've tried everything.
1 System restore..... impossible!: Mc:
2 Malawarebytes, ComboFix, thinking of a virus .... nothing!
3 Uninstalling and reinstalling Windows media center .... nothing!
4 Reinstall and reuninsinstalling of Mediaportal and Nextpvr nothing!
5 Event Log does not show any event at the error msg!
6 Local Security Policy. I entered a new rule with the path to the Wmce ehshell.exe making explicit without restriction .... nothing!
7 Installing all new updates of Win 7 ....
8 Searching on the internet ... not much!
9 Lourdes or a miracle ???
Who can give me a hand before thinking about formatting!

Why is System Restore impossible? Please explain/ Also, a short list of you System Spec's would help.

I think you must be aware that the answer to your problems lies with the way you have installed (and then uninstalled) various different Media Players. You may have several conflicts set up in your sysytem by this: there will probably be leftover garbage in the Registry from it all. Do you have CCleaner, or another Registry Checker? If not, instal CCleaner from here:

CCleaner - PC Optimization and Cleaning - Free Download

and use the 'Registry Cleaner' to find any leftover garbage, such as pieces of software that did not uninstall. You could also carefully explore the registry using <regedit> to find anything which refers to the programmes you installed and then uninstalled.

I don't think the problem lies with any "nasties" on your PC, more that you have a software conflict, caused by installing the alternatives. As a rule, if I am tempted to try another version/alternative to any software I have on my PC, I uninstall the original before installing the alternative. Or you could run it in a Virtual box.

If you try to install Windows Media Center again, have you tried to do it by a right click and "Run As Administrator"?

Have you tried running a sfc/scannow? It'll find and repair any corrupted system files ........ thinking you might have messed something up with all those install/deletions. Run it three times , rebooting after each.

SFC /SCANNOW Command - System File Checker

Also..... have you reset the defaults?

Reinstall Windows. Doesn't sound like the system is in that good of a state, and reinstalling will only take a few hours, probably end up being faster than all of the troubleshooting you're doing.