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. power off your computer
2. power on again right away hold down command and R key, keep holding it until you see a mac osx utilities screen
3. select option to reinstall mac osx and follow the the instruction on the screen.
remember reinstall osx will not delete your data.
If you would like any additional information or have more questions please don't hesitate to ask!
Please remember to only rate my answer when you are 100% satisfied. IF you feel the need to rate bad or poor service, please stop and click on the "Reply to Expert" link with the issue you have. I will be happy to continue further and do everything I can to provide you with the service you seek.
Customer: Hi, Moutain Lion was an online upgrade. Disk wise I only have the standard OSX install disk 1 &2, snow leopard Mac box set disk and a leapord CPU drop in disk...
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
Customer: So I try to reboot pressing command R when I hear the chimes
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
Customer: Ok I'll try.. I'll get back to you...
Customer: Hi, no I just be the same screen white with folder/? Flashing...
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
Customer: Just the mouse icon, unless it takes longer to come up
nothing else show up only the mouse pointer?
Customer: No nothing
Customer: Only 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.
Customer: Is this repairable?
hardware defective cannot be repair, replacement is the only option
Customer: Ok thanks for that....
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
Customer: And it gets installed on this iMac?..
you can even asked them to repair a 2tb hard drive too cost about $150
Customer: Oh ok, not so bad hahaha thank you so much. You've been very helpfull..
please rate my service and have a goodnight
Customer: You too. thanks :)