This information was gathered from different threads and sources.
The first thing you have to do it disable everything in your load order except the New vegas ones. Then you enable FO3, launch the game and see if the menu comes up. If it doesn't, scroll down to the =CONTINUE HERE= part. If there is a menu, continue normally.
Now you want to enable NV with the Fallout3.esm AND 1 Fallout 3 DLC and start the game to see if it's working. If it does work, enable one more DLC till your menu becomes blank. Once your menu becomes blank, we now know that the DLC that you activated before starting the game with a blank menu is corrupt so you'll have to reinstall it
=CONTINUE HERE=
Now that we know which file is causing the main menu to become blank, we have to delete it from the New Vegas directory (including the .bsas) and open the TTW installer. It will recognize that some files are missing (the ones that were corrupt) and will reinstall them. Gladly, it won't take as long because it's not a complete install, instead more of a "repair". Once finished, the TTW installer will ask you to make a FOMOD. Click no. Now head to your TTW directory (The one you installed it to) and select the .esms and .bsas which were corrupt/you deleted. Now you copy them and paste them into the New Vegas/Data folder. Now start your game to see if the main menu is there.
If the main menu is still not there, there's another corrupt file and you have to play around with your load order and enable/disable files. Once you found it, do the thing above to fix it.
I hope this helped people with the blank/no main menu issue as it helped me. Cheers.