Postagem original de: mimi m ,
I had the same problem with startup of my macbook air. I installed a usb modem, then i wanted to play a video which was on my computer and the system got frozen. I restarted the computer and end upwith an apple logo with the spinning wheel under it. I didnt get a recovery CD or usb with my lap top. Had same startup problem sometimes with macbook pro, but then i could use the OSX DVD to restore. Anyway i want to share my experience how i fixed it without losing any data on my computer. Firstly i tried to do a safe mode startup, didnt work. Secondly did a PRAM and SMC reset. Didn't have any success. After the startup chime apple logo would be there then spinning wheel and so would stay for ages. Finally I shut down my computer and started holding down Command + R keys till i got the utilities page. verified the HD report was HD seems to be ok. On the right top side of the toolbar chose the wi-fi and connected it. Then did an online installation of Mountaion Lion again on my Macintosh HD. After installation I let it to restart automatically and voila! It worked ! It started in the same way as i left the desktop to restart. Hope this will help. Good luck to everyone!