Here is a little trick, load the core then go to information>core information then scroll down, it will show what files are required/optional and give the CRC32 and say if they are present or missing.
Seems your renamed bios were incorrect.
There is some great features to that BTW, if a game has very heavy dilthering or just hate PSX dithering like I do load the game and go to core options and go to dithering pattern, switch it on and off and check the gameplay and see if you can spot the difference.
One more thing is set the memory card to Mednafen instead of libretro, they are easier to manage, you can also unplug memory card 2 now, its in the core options as well.
