Hi, Hi, Hi I have the old MacBook Pro. Upgraded to Mountain Lion which completely wrecked the system. So downgraded to Snow Leopard. The updated the combo update. Now stuck on blue screen at start-up. Need help. Greatly appreciated. Thank you.

Question

Hi,
I have the old MacBook Pro. Upgraded to Mountain Lion which completely wrecked the system. So downgraded to Snow Leopard.
Then updated the combo update. Now stuck on blue screen at start-up.
Need help. Greatly appreciated. Thank you.

Answer 1

Downgrade Lion/Mountain Lion to Snow Leopard
  1. Boot from your Snow Leopard Installer Disc. 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.
  2. After DU loads select your hard drive (this is the entry with the
      mfgr.'s ID and size) from the left side list. Note the SMART status
      of the drive in DU's status area.  If it does not say "Verified" then
      the drive is failing or has failed and will need replacing.  SMART
      info will not be reported  on external drives. Otherwise, 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. Set the format type to Mac OS
      Extended (Journaled.) Click on the Options button, set the
      partition scheme to GUID then click on the OK button. Click on
      the Partition button and wait until the process has completed.
  4. Quit DU and return to the installer. Install Snow Leopard.
This will erase the whole drive so be sure to backup your files if you don't have a backup already. If you have performed a TM backup using Lion be aware that you cannot restore from that backup in Snow Leopard (see below.) I suggest you make a separate backup using Carbon Copy Cloner.
If you have Snow Leopard Time Machine backups, do a full system restore per #14 in Time Machine - Frequently Asked Questions.  If you have subsequent backups from Lion, you can restore newer items selectively, via the "Star Wars" display, per #15 there, but be careful; some Snow Leopard apps may not work with the Lion files.