i bought a flash drive to use with both my mac and pcs. it worked just fine but one day for some reason i decided to erase it and reformat it with disk utility. before you ask yes i used the ms-dos format. since then every time i plug it in a windows pc (vista anyways, haven't tried with other operating systems) it asks me to reformat it. if i do that, i can use it, but there's only 200 MB available! (it's a 4GB drive). when i looked in disk utility after reformatting in windows, the other four or so GB were intact. what should i do??