Q: when I push startup button, it is not opening and there appears a white screen with a folder sign. This folder sign has a question mark in it and it shows up and gone continuously.

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That folder means that your Mac was unable to find any startup disk, so your Mac cannot start up. Follow the steps in this user tip > https://discussions.apple.com/docs/DOC-5281

If the steps given in the user tip do not work, you need to replace the hard drive. You can take the Mac to an Apple Store to get it replaced or you can replace it yourself by getting a new 2'5" SATA hard drive or SSD > http://eshop.macsales.com/shop/internal_storage/hard_drives_and_SSD

It probably means your machine can't find the hard drive inside it. It either can't communicate or you re-formatted the drive. Re-formating a drive simply means it changes the "language" it will read and there's only really one format the Mac OS will be read. If you can, try and boot into recovery mode. But it only works with Intel-based Macs as far as I know. To boot recovery mode, hold command and r as soon as you turn on your Mac. Hold that in until you it asks you to select your language and continue from there. When recovery mode is booted, select disk utility. Select "Macintosh OSX" on the left side. If it appears before selecting it, it means the hard drive is communicating with the rest of the machine. You're then going to want to click "verify disk". If anything appears in red, you need to let the machine run a disk repair after it's done verifying. If it's not there at all, then you may need either a new hard drive cable, or the hard drive has failed, and there may be no way of retrieving your data unless it wa backed up via Time Machine or iCloud. If it's there, it must mean your hard drive has been re-formatted. Above the Macintosh HD disk image, there should be the actual name of the hard drive. Click that and select the option to erase and you need to select the correct format or "language" the Mac OS needs, and that format is "Mac OS Extended (journaled). When it is finished, restart the machine and as soon as it turns on, hold command r again. This time when recovery mode is booted, click "Reinstall OSX". It's going to need an internet connection (wired or wireless) to download the OS to your machine.

If your hard drive needs to be replaced, find out what make, model, and year it is along with your processor and current RAM configuration. If you have the original box it came in, it'll have all the information you'll need to find replacement parts. Once you have found out this information, use another computer or wireless device and go to www.crucialmemory.com and contact them with what you need for what machine and they'll help you find what will work with your machine. I HIGHLY recommend an SSD since they are 4x faster and are far more durable, thus making them super reliable. I would also suggest a backup hard drive. I suggest something with more storage than what your machine will have. I have one of those 2TB time capsules from Apple and its just awesome for keeping data safe.

Good luck!