I apologize for any inconvenience this problem has caused you.
The startup screen can be turned off by unticking the "Show the Welcome page the next time Visual Studio is started" tick box
at the bottom of the startup screen.
If you have done this and are still seeing the startup screen then you will need to set the NoVSNETSplash reigstry value under the HKEY_CURRENT_USER\Software\Innovasys\DocumentX5 key to "True". This value is created after Visual Studio (with the Document! X addin enabled) has been opened at least once.