This has been talked about extensively on Scroll Saw Village.
Being an Administrator solves the problem but I found that you have to save the ttf to a file and then right click and install to all users.
Some fonts come in a Zip and when you say extract the ttf is there but when you click it does not give the all users.
If you save to a folder (or desk top) and then click on that file the install to all users comes up.
I have a couple of laptops and this works on both regardless is I am the administrator of not.