hi all i was working on my macbook air and it suddenly lagged so i restarted it. now everytime i turn it on i get the no bootable device please insert any key to continue. so I tried the Alt key and sometimes the mac hd dsnt show up and sometimes when it does i click on the arrow and when the apple sign appears it loads for a few minutes and then it changes into another sign like the STOP sign i think? so i dno wts wrong with the laptop!! please help me asap thanks!!