i agree with keldorn, his/her comp may not be powerful enough to load all the textures (so u can see it) fast enough for when the lag stops for a second it, it just shows black, but thats my guess, it could be just cause his/her vid card isnt big enough (MB-wise) or the system doesnt have much RAM or is perhaps too slow
these are just guesses, but if updating everything helps it could be just a driver bug
EDIT: randomlycrazy, in case u didnt really get anything i said, i basicly said u may have to upgrade ur computer abit, or u may have to update some computer things
hope ya have fun though picking up crystals as soon as u can play good enough