Somehow my task bar got moved from being horizontal along the bottom of my screen to being vertical along the right-hand side.  I can occasionally drag it so that it will return to the original position along the bottom, but most times it won't move at all.  Even when I can successfully drag it, it never stays down there; everytime I log off and then log back on it is right back to being vertical.  How can I get it to the bottom and keep it there?