If the clipboard function is grayed out it's usually because it has been disabled through a policy. Have you ever used any of the Windows 10 anti-spy programs like O&O Shutup10?
You can remove any of the policies by editing the registry or making the following registry file.
Open Notepad and copy/paste the following content, then save as type All Files (*.*) name clipboard_fix.reg
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\System]
"AllowClipboardHistory"=-
[HKEY_CURRENT_USER\Software\Microsoft\Clipboard]
"EnableClipboardHistory"=-
Once you've created the file, double click on it and allow it to merge with the registry, then reboot for the changes to be applied.