Question marks on all my icons

Please help me - I have a Mac Pro with OS X (version 10.5.8)

My problems are two fold. First, when I click on any of the icons on my dock, a light grey question mark appears over the icon and won't let me open it. I'm also unable to open any of the folders on my desktop. I'm unable to open system preferences.

When I try to open my applications, I get a message that says "The folder applications could not be opened because you do not have sufficient access privileges." I've been given all the access privileges on the computer so I'm not sure why I'm getting this message.

Thank you for any help you can provide. I greatly appreciate it.

Try booting with your install disk, then Not continuing the install, but instead choosing Disk Utility from the Finder menus. Use Disk Utility to repair the disk.

An alternate way to achieve this is to do a Safe Boot:
Mac OS X: Starting up in Safe Mode
Mac OS X: What is Safe Boot, Safe Mode?

Let us know the result.

I just booted up the computer in Safe Mode and now I don't even see any of the icons at all. All I see are question marks all across my doc. Now what do I do?

Did you by chance move your home folder or rename it?

No, I didn't rename or move my home folder.

OK, that's fine. The symptoms you described can occur when the home folder is moved or renamed. Try this: Create a test account and give it admin privileges. Log off and log on to the new account. Is the same thing happening?

do disk utility and repair permissions off the install CD and reboot, and see if that helps