Blinking folder with question mark when I power on laptop.

There are four general causes of this issue:

1. The computer's PRAM no longer contains a valid startup disk setting when there aren't any problems with the disk itself. This can be checked for by pressing the Option key and seeing if the drive appears.

2. The internal drive's directory structure has become damaged. This requires usage of an alternate bootable system to perform the repair.

3. Critical system files have been deleted. This requires usage of an alternate bootable system to reinstall them.

4. The internal drive has died or become unplugged. This is the most likely case if the computer took a sharp impact or there are unusual sounds coming from the hard drive's location.

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It varies depending on which Mac you have and whether or not you can access the computer's recovery partition or a Mac OS X install DVD.

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Does it means that it needs to be taken to the apple store for service? How long does it takes usually? Tq

After a preliminary assessment (which in turn depends on having a prearranged appointment or there being few people in front of you in the queue), depends on the damage. If simple, like a corrupt OS, they may have time to fix it in your presence. If severe, like a bad drive or a damaged logic board, has to be sent to the next level of support and can take several days or weeks.

First try getting in Recovery Mode. Command-R prior to the startup chime to try with the internal drive, Command-Option-R to try thru the Internet on Apple's servers. Once going, start Disk Utility and see if the OS X volume is still around. Holler back for details if needed.

hey buddy i am new to use apple macbook air and in my case i think some how i formatted my macbook air and now i see white screen with grey folder with a question mark , can any one help please .