Open in wrong drive and/or getting stuck during startup

Question

Please help!
My Mac OS X (10.4.11) has two drives: one for normal use and one for backup. For some reason my Mac keeps opening up in the backup drive. I go to System Preferences and click on Startup disk, and tell it to restart in the main drive, and it still opens up in my backup. It will eventually let me over after a dozen tries (give or take a few).
Once in a while it will freeze up during startup, get stuck during loading, or the fan will go into overdrive and I get nothing but a gray screen.

Answer 1

Whew! Sounds like a potential combination of needing to repair the drive(s) and zapping PRAM. What exact model of computer (OSX is the operating system, not the computer model)?
Boot from the installer disk, select language if applicable, choose utilities, run Disk Utility and verify (and repair if necessary) the drive. You can verify a drive from DU on your main drive while booted but I have found this can result in incorrect reporting of errors. To repair your drive you have to run it from a drive other than the boot drive anyway.
Next, boot from your drive in [Safe Mode|http://docs.info.apple.com/article.html?artnum=107393] and repair permissions. You can repair permissions while booted from the installer disc but this uses the permissions configuration on the installer disc which may be out of date if you have run any updates on your computer. Booting your computer to Safe Mode restricts the number of things running on your computer while permissions are being run and does a bit of spring cleaning at the same time.
[Resolve startup issues and perform disk maintenance with Disk Utility and fsck|http://docs.info.apple.com/article.html?artnum=106214]
[Using Disk Utility in Mac OS X 10.4.3 or later|http://docs.info.apple.com/article.html?artnum=302672]
[Disk Utility's Repair Disk Permissions|http://docs.info.apple.com/article.html?artnum=25751]
From BDaqua (couldn't have said it better):
"Try Disk Utility
1. Insert the Mac OS X Install disc that came with your computer (Edit: Do not use this disc if it is not the same general version as what you have currently on your computer, e.g. use a Tiger disc for a Tiger drive, not a Panther disc), then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu. (In Mac OS X 10.4 or later, you must select your language first.)
Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.
3. Click the First Aid tab.
4. Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
5. Select your Mac OS X volume.
6. Click Repair. Disk Utility checks and repairs the disk.
Then Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes."
Once all is clear, you might need to reset PRAM.
[Texas Mac Man's PRAM, battery, PMU tutorial|http://www.geocities.com/texas_macman/pram.html]
[Apple's PRAM reset directions|http://docs.info.apple.com/article.html?artnum=2238]
If this helps you may also need to get a new PRAM battery but we need to know more about your computer hardware.