Hello Friesjh,
Thank you for posting your query in Microsoft Community.
I understand that you are getting a slow performance issue with the system and I appreciate your efforts taken to resolve the issue.
No matter how fast or shiny computers might be when they're new, they all seem to get slower over time. That state-of-the-art PC you bought last year might not feel like such a screamer after you install a dozen programs, load it with antispyware and antivirus tools, and download untold amounts of junk from the Internet. The slowdown might happen so gradually that you hardly notice it until one day your system stops responding.
So, I would suggest you to try the following methods that might help you to optimize your windows for better performance.
Method 1:
I would suggest you to run the System Maintenance troubleshooter and check if it helps.
a) Press the ‘Windows + W’ key on the keyboard.
b) Type troubleshooter **** in the search box and then press ENTER.
c) Select Troubleshooting. Click on view all and select System Maintenance.
d) Click next and follow the on-screen instructions.
Note: I would suggest you to disconnect all the external devices other than mouse and keyboard and check if it helps.
Method 2:
Delete programs that you never use. Maybe you thought you might use the software someday, but never did. Uninstall it and see if your PC runs faster.
Uninstall, change or repair a program
I see you have already tried the Clean boot process while troubleshooting which concludes it not to be an issue due to some third party software conflict.
Method 3:
Optimize your drive for better performance. Refer to the following link to optimize or repair your drive.
Improve performance by optimizing your drive
Important: While performing chkdsk on the hard drive if any bad sectors are found on the hard drive when chkdsk tries to repair that sector if any data available on that might be lost.
Method 4:
If your PC is running slowly, it's possible that it's infected with a virus or spyware. This is not as common as the other problems, but it's something to consider. Run the Microsoft Safety Scanner for check for any viruses/malware on the computer. Refer to the following link:
http://www.microsoft.com/security/scanner/en-us/default.aspx
Note: The Microsoft Safety Scanner expires 10 days after being downloaded. To rerun a scan with the latest anti-malware definitions, download and run the Microsoft Safety Scanner again. Any data files that are infected may only be cleaned by deleting the file entirely, which means there is a potential for data loss.
Hope this information is helpful. Do let us know if you need any further assistance, we'll be glad to assist you.