Which Toolbar is it? You may have dragged your toolbar so far off-screen that you simply can't see it. Tends to be the problem for people who have it checked under View.
Unlock your taskbar and close other windows and try to see if the toolbar isn't just hidden.
If you can't find it anywhere on your monitor, you can open Command Prompt (right-click it and Run as Administrator) and use this to reset the toolbars:
reg delete "HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\Paint\General-Summary" /f