hi,when you have a white screen with folder and question mark meaning the system did recognize any core files to boot to osx operating system.two things might caused your problem: corrupted osx operating system or defective hard drive.what you can do is reinstall Mountain Lion, if the installed go through without a problem then your problem is corrupted osx operating system. now if you got an error during installation process or system didn't recognize the internal hard drive to install mac osx operating system then you have a defective hard drive and need replacement.500GB sata 2.5" hard drive cost about $80, you can bring to apple store to have them installed it.follow the step below to reinstall Mountain Lion 10.8:1.
1. power off your computer2. power on again right away hold down command and R key, keep holding it until you see a mac osx utilities screen3. select option to reinstall mac osx and follow the the instruction on the screen.remember reinstall osx will not delete your data.
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mountain lion install a hidden partition on your hard drive when you installed it
if you try command + R and still cannot get into mac osx utilities screen to reinstall 10.8 Mountain Lion that mean the internal hard drive is defective or dead
* hidden partition that include all the files to reinstall osx
reboot press and hold both command and R keys, continue to hold it until you get into a mac osx utilities screen
remember to do it right away after you reboot or system power back on
try this:power off your computer then power on again right away hold down option (alt) key, keep holding it until you see a boot menu
boot menu it just a white screen but you can see the mouse pointer
now in the boot menu do you see any name or icon show up?
look something similar to this screen --->> http://www.clemson.edu/ccit/mac_software/images/choose.jpg
nothing else show up only the mouse pointer?
unfortunately, that mean the internal hard drive on your imac is completely dead thats why the computer didnt even recognize or detect it.
hardware defective cannot be repair, replacement is the only option
500gb hard drive cost about $80
so it a good time to upgrade to a bigger storage so you got more space with help your system run faster
with = will
you can even asked them to repair a 2tb hard drive too cost about $150
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