Since this option used to work and you did not change it then something changed it for you, this can be either malware or a hardware/program installation:
1. so first ensure your system is clean, download MBAM and SAS, links below.
2. what is your current antivirus?
3. any errors in Event Viewer that relate to this issue?
4. need some system info, follow instructions below:
Click Start, Run and in the box enter:
msinfo32
Click OK, and when the System Summary info appears, click Edit, Select All (Ctrl-A), Copy (Ctrl-C) and then paste (Ctrl-V) the information back here in your next reply.
You can edit out any personal information.
Download, install, update and do full scan with these free malware detection programs:
Malwarebytes (MBAM):
http://www.malwarebytes.org/products/malwarebytes_free
SUPERAntiSpyware: (SAS):
http://www.superantispyware.com/
Remove all found, reboot, and run again until scans run clean, these can be removed afterwards if you so choose.
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after system is clean, then we can work more on enabling if still does not work.