Hello,
You may try the following to enable/fix your Quick Access again;
1. In the search box on your taskbar or Start menu, type regedit, and press Enter to open Registry Editor.
2. If prompted by UAC, click/tap on Yes.
3. In Registry Editor, navigate to the location below.
HKEY_CLASSES_ROOT\CLSID\{679f85cb-0220-4080-b29b-5540cc05aab6}\ShellFolder
4. If you have not already, you will need to first change the owner of the ShellFolder registry key in the left pane to be the Administrators group.
5. If you have not already, you will need to set permissions of the ShellFolder registry key in the left pane to "Allow" the Administrators group "Full control".
Screenshot:
http://prntscr.com/8emom5
6. In the right pane of ShellFolder, double click/tap on Attributes to modify it.
7. Do number 8 (remove) or number 9 (add) below for what you want.
8. Type in a0600000, and click/tap on OK
If you have not already, set File Explorer to open to This PC by default instead of Quick access. If you have a 64-bit Windows 10, then repeat number 4 to 7 above for the registry location below. This step is to add or remove Quick access from the "Open" and "Save as" type dialog in 64-bit Windows 10. This step is not for 32-bit Windows 10.
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Classes\CLSID\{679f85cb-0220-4080-b29b-5540cc05aab6}\ShellFolder
9. NOTE: This is the default setting.
Type in a0100000, and ensure "Hexadecimal" is selected, click/tap on OK.
10. When finished, close Registry Editor.
11. Sign out and in of Windows or restart the PC to apply.