my computer does not boot up. I cannot access the recovery disk. cmd r doesn't work. I tried safe mode and doesn't work. I get a white screen and then it freezes.

You can try reinstalling OS X if the drive has not failed. If your computer originally had Snow Leopard installed then boot from your Snow Leopard DVD, open Disk Utility from the Utilities menu in the menubar, erase the hard drive if you can. Reinstall Snow Leopard.

If your computer came with Lion or later pre-installed when it was new, then do the following:

Install OS X Using Internet Recovery

Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.

Boot to the Internet Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND-OPTION- R keys until a globe appears on the screen. Wait patiently - 15-20 minutes - until the Recovery main menu appears.

Partition and Format the hard drive:

1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your newly installed hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed. Quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Install button. Be sure to select the correct drive to use if you have more than one.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

This should restore the version of OS X originally pre-installed on the computer.

If the hare drive cannot be repaired or reformatted, then you will need to have it replaced.

Try a SMC reset:

https://support.apple.com/en-us/HT201295

If no success, make an appointment at an Apple store genius bar for a FREE evaluation.

Ciao

Did your computer come with Snow Leopard or earlier installed when new? If so then do this:

Clean Install of Snow Leopard

Be sure to make a backup first because the following procedure will erase

the drive and everything on it.

1. Boot the computer using the Snow Leopard Installer Disc or the Disc 1 that came

with your computer. Insert the disc into the optical drive and restart the computer.

After the chime press and hold down the "C" key. Release the key when you see

a small spinning gear appear below the dark gray Apple logo.

2. After the installer loads select your language and click on the Continue

button. When the menu bar appears select Disk Utility from the Utilities menu.

After DU loads select the hard drive entry from the left side list (mfgr.'s ID and drive

size.) Click on the Partition tab in the DU main window. Set the number of

partitions to one (1) from the Partitions drop down menu, click on Options button

and select GUID, click on OK, then set the format type to MacOS Extended

(Journaled, if supported), then click on the Apply button.

3. When the formatting has completed quit DU and return to the installer. Proceed

with the OS X installation and follow the directions included with the installer.

4. When the installation has completed your computer will Restart into the Setup

Assistant. After you finish Setup Assistant will complete the installation after which

you will be running a fresh install of OS X. You can now begin the update process

by opening Software Update and installing all recommended updates to bring your

installation current.

5. If you are planning to sell or give your computer away, then do the following:

After you reformat your hard drive and reinstall OS X, the computer restarts to a

Welcome screen and asks you to choose a country or region. If you want to leave

the Mac in an out-of-box state, don't continue with the setup of your system. Instead,

press Command-Q to shut down the Mac. When the new owner turns on the Mac,

the Setup Assistant will guide them through the setup process.

Download and install Mac OS X 10.6.8 Update Combo v1.1.

Hi. Try booting to single user mode. Command S If you get to it you can use it to repair disk. https://support.apple.com/en-us/HT203176