I’ve been trying to get 3DO games running using the 4DO core and having no luck whatsoever. Yes, I have the BIOS file in the system folder and the location correctly set in the settings. I’ve tested both my iso and the bios using the standalone exe version of 4DO to make sure they work but every time I try to load the same iso using the core in RetroArch it just crashes back to the desktop. 
Works for me. You can check to make sure your BIOS is being recognized by loading the core but not a game, then go to information > core information and it will tell you which BIOS it needs and whether it’s finding it or not.
Currently updated core is broken. I downloaded an older build of the 4DO core and it works fine.
where did you get do you have a link?
It’s fixed in the latest nightly version of the core.
http://buildbot.libretro.com/nightly/windows/x86_64_w32/latest/4do_libretro.dll.zip
thanx for the information try it out
so will i need to download the nightly version or can i use this core on the stable version?
It will work on stable.