Access Denied for D and C Drives due to accidental restrictions

Im using Windows 10 and i got a problem: Access denied to both drives C and D...running cmd is also restricted...system restore is also erratic...The cause: I right-clicked my C drive and click properties, i click security, denied authenticated users in the allow and deny options, and now im denied to access my both drives...My original plan: I just want to restrict the guest account not to access my C and D drives...to my surprise i can still access my desktop files...

Now, when i right click my C or D drives and click security, the only option i see is Advanced, and when i click it then i was given three options: permissions, Auditing, and Effective Access with Continue options, then Unable to display owner with a Change option...WHAT SHALL I DO? Please help me for the grades of my students were saved in my D drive and I need to submit them not later than next week...My gratitude in advance

Pls see if these help:
Remove 'Access Denied' error when accessing files or folders in Windows
How to take Ownership of Files & Folders in Windows 10/8

I just want to say that this absolutely saved my life!

To elaborate a bit and make it a tiny bit clearer:
if you have ever shared the folder/file in question, go to your task manager, and go to your 'services'.
Right click on "WMPNetworkSvc" and stop the service (this will take a few seconds).
Attempt to delete the file, if it doesn't work, try looking in the descriptions and stop any process that has the word 'sharing' in it.
Make sure to reenable the services once the file has been deleted!

Really hope this helps.