How exactly did you launch your games? FMCB or it's commercial "predecessor" can't run PS2 games without another 3rd party loader.
I have softmodded my Mem Card, but I seem to have problem playing games. All of them boot, but they end up having problems with either graphics, sound or both. In some the graphics shiver or appear distorted, in others, the sound sometimes comes otu as bleeps. This is an example of what is wrong :
If you're playing from a backup disc, can that disc work properly when launched by other methods (Or played with another console)?
If you're playing your games via OPL then your disc image may be corrupted, or the current implementation of OPL isn't compatible with your game.
Unmodified SCPH-77006 with SM 3.6
SCPH-39006 with M-chip modchip, SCPH-10281 NA and refurb Seagate 80GB HDD
SCPH-10000 v1.00 with SCPH-10190 PCMCIA NA and SCPH-20400 HDD unit