Microsoft's Autouns (available here) is a very powerful (and potentially dangerous) tool that quickly shows most everything about applications, drivers and libraries that startup on boot. With the tool you can view locations, properties and even delete these entries (hence the dangerous comment).
This may reveal some items that cannot be found or uninstalled. One example was "sysmenu.dll" apparently a type of start menu for Windows 8 but upon updating to Windows 8.1, the computer boots with an error. Autoruns showed the offending boot item which was easily deleted...
In the above snapshot is an item highlighted because the startup item's file is missing. Upon investigation we can see that item was in a temporary folder so it could be safely deleted.