Nikon d200-manual mode

when set on manual exposure mode, my camera won't let me shoot faster than 250. i adjusted everything i could and it won't move. in the display screen, it reads x250. it's never done this before and i can't make it move/change. i was shooting baseball on a bright, sunny day with an iso of 200. should've been able to shoot around 5.3 @ 2000. any idea on what x250 means and how i can fix it? i don't think i've changed anything in the shooting menu that i can tell. can't find anything in the manual either.
thanks.
donna tinsley