I think you have two Possibillities:
First your Control Key is broken.
Second there are Macros assigned to these Shortcuts in the Access File (or even In Access it selfs) so Windows doesn't know which one it should do the System one (copy/paste undo ...) or the Macro.
To check First: Use the shortcut in an Application like Word where you knew it has functioned before.
For the Second: Have a look at the Menu Entry you should see the Shortcut next to it. Or go to the Create tab, in the Other group, click Macro and see if there are any Macros.
If this doesn't bring you to a solution, add some more details like Operating System and Access Version you're using.