imac doesn't boot

[satsagat]

Hello

i've bought an imac last year, it has exactly a year now.

since yesterday it doesnt want to boot. it starts, shows the white screen with "the apple" in the beggining and then stops any action with the empty blue screen only. It boots for only few seconds actualy and then freezes.
i've tryed to turn it off and on several times ,it doesn't change a thing.

the night before i believe, i did do smtg that could be the cause...
as i saw an icon 'public' on the finder and didnt like anything to be public from my computer, i put "forbidden" i think or somthing like that at the "public" profile/user.

could that be the cause ? if not, would you please have any idea to help ?

thank you so muc

 

[ElDiabloConCaca]

the night before i believe, i did do smtg that could be the cause...

What, exactly, is "smtg?"

as i saw an icon 'public' on the finder and didnt like anything to be public from my computer, i put "forbidden" i think or somthing like that at the "public" profile/user.

Do you mean you changed permissions on that folder? The "Public" folder does not indicate in any way, shape, or form that anything on your computer is "visible to the public." I think you're misunderstanding what the "Public" folder is and what it's used for. Trust me, out of the box, your computer is not sharing a damn thing with anyone, anywhere, and will not do so unless you specifically instruct it to do so.

Try booting in Safe Mode by holding down the Shift key as the system boots, then open "Disk Utility" and run a "Repair Permissions" procedure.

If that doesn't fix it, try booting from your OS X CD/DVD that you used to install OS X (or was shipped with the computer) and use Disk Utility to repair the permissions from there.