Please help me! My mac air stays on the apple logo white screen.

what can I do when I turn on my Mac air, and it stays on the white screen which has the apple logo? How can I reinstall or anything I can do to fix it ?

Thanks alot.

Which MBA do you have and what version of OS X is it running? Do you own an Apple external optical drive for the MBA?

I do not have it. what should I do ?

I believe if you have lion osx and the thumb drive and back up, you might be able to install new osx and using the backup to install the application and data to revive your systems, just my 2 cents.

in my case, how can I reinstall new osx? like put in the thumb drive and restart the mac?

if you have lion osx on thumb drive and backup drive in external enclosure then you are in good shape.
I understand there is no dvd drive to put in the osx and application in mba,
the idea is to insert the thumb drive in usb port, and press option key as soon as the chime of the mba boot up. then the screen will guide you thru how to get you back the mba working.
Or you can get an external optical drive and use the cd disks from apple to install to your mba.