Most games work perfect (100+) but around about 5 of them will not even boot past the sega logo, the furthest is the second 'stop', for example the "press a to continue without memory card" screen.

Now i've searched and found that a scratched or dirty disk can cause this, but these disks are mint. No trace of problem at all, I even removed the mod chip that I inserted to try and make them work (no idea why my logic made me do this)

The games effected are: Virtua Fighter 3tb, Buzz Lightyear, House of the dead 2, chu chu rocket, and Plasma sword.

Any ideas?

P.S. I just bought another copy of VF3tb and also has the problem.