Xp wont start

Hello,
thers sum problem...i was working on computer when suddenly it restarted and after that the same message "press shift-tab key....."is comin and i dnt know what to do. when i press shift tab key it says" 1. local drive boot, 2)then, try network boot first..."watz that , what can i do to start my xp...????n i even didnt install sum new hardware which might be causing the problem plz help:(