How to solve Error 5: Access is denied for Diagnostic Policy Service
So many people facing this problem in Diagnostic Policy Services
“I cannot connect to any network, troubleshooter found that “The Diagnostics Policy Service is not running”
so I try to start it in services.msc but error with “Windows could not start the Diagnostic Policy Service service on Local Computer”
and “Error 5: Access is denied”
The error means “Access is denied”. This may happen if the “MpsSvc” account doesn’t have the necessary permissions for the related registry keys.
Please follow the below steps or click below link or :
http://support.microsoft.com/kb/943996
System Restore affects Windows system files, programs, and registry settings. It can also make changes to scripts, batch files, and other types of executable files created under any user account on your computer. System Restore does not affect personal files, such as e-mail, documents, or photos, so it cannot help you restore a deleted file. If you have backups of your files, you can restore the files from a backup.
System Restore automatically recommends the most recent restore point created before a significant change, such as installing a program. You can also choose from a list of restore points. Try using restore points created just before the date and time you started noticing problems. The descriptions of the restore points that are created automatically correspond with the name of an event, such as Windows Update installing an update. System Restore returns your computer to the state that it was in before the restore point that you chose
Before you start System Restore, save any open files and close all programs. Once you confirm your restore point, System Restore restarts your computer.
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Open System Restore by clicking the Start button
. In the search box, type System Restore, and then, in the list of results, click System Restore. 
If you’re prompted for an administrator password or confirmation, type the password or provide confirmation.To undo the changes System Restore makes
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Open System Restore by clicking the Start button
. In the search box, type System Restore, and then, in the list of results, click System Restore. If you’re prompted for an administrator password or confirmation, type the password or provide confirmation. -
Click Undo System Restore, and then click Next.
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Review your choices, and then click Finish.
If System Restore doesn’t fix the problem, you can undo the restore operation or try choosing a different restore point. If System Restore doesn’t display any restore points to choose from, make sure you have system protection turned on and that you have at least 300 MB of free space left on your hard disk if it is 500 MB or larger, or have at least 50 MB of free space if your hard disk is smaller than 300 MB. If System Restore doesn’t fix the problem, you can also try an advanced recovery method.
For the “Diagnostic Policy Service” service, the issue may occur when the account Trustedinstaller is missing the permissions for the key below:
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HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DPS\Parameters
The permission needed is: Full Control, Read. Do follow the resolution given in the above link.
You can also try performing a system restore. Refer the below link as in how to perform a system restore:
http://windows.microsoft.com/en-US/windows7/System-Restore-frequently-asked-questions
Hope this information helped!