MBP won't turn on. Stuck at apple icon loading screen =[

Question

So basically, I don't really understand why, but randomly yesterday my computer stopped being able to boot to Mac. It happened after I switched to Vista via Bootcamp, and then when I was finished, I tried going back to my MacHD, but it just gets stuck at the screen with the Apple Icon and loading ring.
I tried inserting the BootCD and repaired the MacHD with Disk Utility, but the same results.
Any idea what I should do? I have no idea what could have happened.

Answer 1

You can try this:
Boot into single-user mode. After startup is completed you will be in command line mode and should see a prompt with a cursor positioned after it. At the prompt enter the following then press RETURN:
/sbin/fsck -fy
If you receive a message that says "*** FILE SYSTEM WAS MODIFIED ***" then re-run the command until you receive a message that says "** The volume (nameofvolume) appears to be OK." If you re-run the command more than seven times and do not get the OK message, then the drive cannot be repaired this way.
If you were successful then:
/sbin/mount -uw /
rm -rf /System/Library/Caches/*
rm -rf /System/Library/Extensions.mkext
rm -rf /Library/Caches/com.apple.ATS
rm -rf /Library/Caches/com.apple.LaunchServices*
reboot
Please write down the above lines exactly so you can enter them correctly otherwise you could cause some serious problems.
If this doesn't work, then do the following:
How to Perform an Archive and Install
An Archive and Install will NOT erase your hard drive, but you must have sufficient free space for a second OS X installation which could be from 3-9 GBs depending upon the version of OS X and selected installation options. The free space requirement is over and above normal free space requirements which should be at least 6-10 GBs. Read all the linked references carefully before proceeding.
1. Be sure to use Disk Utility first to repair the disk before performing the Archive and Install.
Repairing the Hard Drive and Permissions
Boot from your OS X 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 Installer menu (Utilities menu for Tiger.) After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported, then quit DU and return to the installer.
2. Do not proceed with an Archive and Install if DU reports errors it cannot fix. In that case use Disk Warrior and/or TechTool Pro to repair the hard drive. If neither can repair the drive, then you will have to erase the drive and reinstall from scratch.
3. Boot from your OS X Installer disc. After the installer loads select your language and click on the Continue button. When you reach the screen to select a destination drive click once on the destination drive then click on the Option button. Select the Archive and Install option. You have an option to preserve users and network preferences. Only select this option if you are sure you have no corrupted files in your user accounts. Otherwise leave this option unchecked. Click on the OK button and continue with the OS X Installation.
4. Upon completion of the Archive and Install you will have a Previous System Folder in the root directory. You should retain the PSF until you are sure you do not need to manually transfer any items from the PSF to your newly installed system.
5. After moving any items you want to keep from the PSF you should delete it. You can back it up if you prefer, but you must delete it from the hard drive.
6. You can now download a Combo Updater directly from Apple's download site to update your new system to the desired version as well as install any security or other updates. You can also do this using Software Update.