Have you booted off the Install Disk by holding the *d key* down at boot-up, (not the c key), and run the extended Apple HW Test? Some Install disks require holding the Option key at bootup to select the AHT. Some Macs came with separate AHT CDs.
One way to test is to Safe Boot from the HD, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, Test for action in Safe Mode...
Reboot, test again.
If it only does it in Regular Boot, then it is some 3rd party add-on, Check System Preferences>Accounts>Login Items window to see if it or something relevant is listed.
Also look in these if they exist, some are invisible...
/private/var/run/StartupItems
/Library/StartupItems
/System/Library/StartupItems
Could be many things, we should start with this...
"Try Disk Utility
1. Insert the Tiger Mac OS X Install disc that came with your computer, 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."
http://docs.info.apple.com/article.html?artnum=106214
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 finishes.
The usual reason why updates fail or mess things up, or things don't load/run, is if Permissions are not fixed before & after every update, with a reboot... you may get a partial update when the installer finds it doesn't have Permissions to change one obscure little part of the OS, leaving you with a mix of OS versions.
Some people get away without Repairing Permissions for years, some for only days.
If Permissions are wrong before applying an update, you could get mixed OS versions, if Directory is the slightest messed up, who knows!
If many Permission are repaired, or any Directory errors are found, you may need to re-apply some the latest/biggest updates again, or even do an A&I if you have enough free disk space.
The combo update for PowerPC-based Macs...
http://www.apple.com/support/downloads/macosx10411comboupdateppc.html
The combo update for Intel-based Macs...
http://www.apple.com/support/downloads/macosx10411comboupdateintel.html
Repair Permissions before & after re-install, then reboot again each time.
If all the above fails, then it appears to be time for a relatively painless Archive & Install, which gives you a new/old OS, but can preserve all your files, pics, music, settings, etc., as long as you have plenty of free disk space and no Disk corruption, and is relatively quick & painless...
http://docs.info.apple.com/article.html?artnum=107120
Just be sure to select Preserve Users & Settings.
I only use Software Update to see what is needed, then get them for real via...
http://www.apple.com/support/downloads/
That way I can wait a week or so, check the forums for potential problems, and get Permissions & such in order before installing.
If it appears to be time for An Archive & Install, which gives you a new OS, but can preserve all your files, APPs, pics, music, settings, etc., as long as you have plenty of free disk space...
http://docs.info.apple.com/article.html?artnum=107120
Be sure to use Preserve Users & Settings.
