my dc wont play some back-ups but plays others. PLEASE HELP!!!

i have recently aquired new burned dc games, but they dont work. they are all self bootable and my supplier thinks thats the reson they dont work, but i have Q3 and 4x4 evo and the both work and are self booting.
but for some reason my dreamcast isnt running other self booting ones. i though that my lens might be scratched, so i bought a $90 lens cleaner, still doesnt play. i dont know whats going on. PLEASE HELP.