The solution:
For those who still have this problem, this is the solution:
1 - Start the mac holding 'option';
2 - Choose the recovery boot disc;
3 - Select Disc Utility option;
4 - Select the disc where os x is installed;
5 - Click 'Fix disc permissions' button;
6 - Wait till it's done;
7 - Restart you mac in normal mode;
8 - Problem solved (At least for me and the guy that told me to do this).
For those who still have this problem, this is the solution:
1 - Start the mac holding 'option';
2 - Choose the recovery boot disc;
3 - Select Disc Utility option;
4 - Select the disc where os x is installed;
5 - Click 'Fix disc permissions' button;
6 - Wait till it's done;
7 - Restart you mac in normal mode;
8 - Problem solved (At least for me and the guy that told me to do this).