SentaiBrad said
Under the Emulators Page, edit RetroArch. Check the Associated Platforms page, there are three columns. On the left make sure that the Turbografx 16 system name matches the name on the left pane in LaunchBox. Then check each of the Sega consoles. Sega Mastersystem, Sega Genesis, Sega Game Gear, Sega CD, etc.
Once you know the names all match, check the middle column. The middle column for Turbografx 16 should be
-L "cores\mednafen_pce_fast_libretro.dll"
The other Sega systems (except 32X, Saturn and Dreamcast) should be
-L "cores\genesis_plus_gx_libretro.dll"
Now I'm at work, I come home just check the setting again, although I'm pretty sure they're correct