Dock doesn't disappear before reboot
Have you tried removing some of the items from your dock?  You can always add them back later. Also go under your Apple Icon in the top left corner to the force quit option and see if there is a application open somewhere you're not aware and force quit it.  Finally, look in your system preferences for the Dock. You can choose to hide the Dock to only appear when your cursor goes to the bottom of the screen. I doubt that would solve your problem though.  I have my Dock on the left side of my screen and it is hidden, that way I can see the entire screen and only access the Dock when I need to open an application.  Good luck.