Make sure you are really pressing the F and not the G key.
Shortcuts don't just stop working and changing a shortcut is generally not something you do by mistake without knowing it.
You can also go to File > Defaults > Load Factory Settings. Then you are certain everything works as expected.
Sounds a little suspicious that the F key is right beside the G key that activates the move operation. That's like catching the G key in the living room, next to the body of the F key, with the murder weapon at hand, and the G key has always hated the F key. Really really really make sure you're not pressing the wrong key.