Are you saying that using the Menu does not work or are you saying that the keyboard shortcut does not work.
Try adding a solid to the comp that is something like 200 X 200 pixels. Then try the shortcuts. If the solid does not fit to the comp then there is something going on. If you are trying to fit a masked layer or a text layer or a shape layer then this won't work. The fit to comp only works on layer dimensions and shape layers, text layers and masks do not take their size from the size of the shape, the mask, or the text so the shortcuts will not work.
If the Menu works but the keyboard shortcuts don't work, and clearing out the preferences files does not fix the problem then there may be something wrong with your keyboard mapping. You need to test the other shortcuts like Alt/Option + p to set a position keyframe, Ctrl/Cmnd + D to duplicate a layer. If none of these work then there is something wrong with your keyboard settings. Open up your control panel and make sure everything keyboard related is normal.