Flashing question mark at start up

If by flashing globe you mean spinning globe (often a colored beach ball), there are several possible reasons. The spinning beach ball happens when a operating system command cannot be completed. The computer is frozen/stuck in a process that it can't complete.
Most often the cause is faulty or missing information on the hard drive. Running Disk Utility will often fix it. You may need to start the computer from your OS install disk and rather than install find Disk Utility in the pull down menu and run it on your hard drive.
The spinning ball could also be caused by insufficient RAM memory to even run the operating system. It could also be caused by hardware problems which can be diagnosed with the Apple Hardware Test found on the disks sold with the machine.
If you truly mean a flashing round globe, I have never seen such a figure. Flashing question marks or flashing circle with a slash through it means the mac cannot find a bootable hard drive. Your hard drive may have died or become corrupted. To see if you hard drive is defective, again run Disk Utility by booting off an install CD or another hard drive with a compatible MacOSX operating system to diagnose.
Try running the repair disk program under the general tab of the Disk Utility program.

Your hard drive may have crashed or it's settings have changed so it is no longer recognized as a startup (boot) drive. Try starting from your original operating system CD. (or borrow one). Press the C button at power up to force your computer to start from the CD.
Once started, don't install the operating system. Go to the pull down menu's and select Disk Utility. If Disk Utility sees your hard drive, select it and run the repair disk program. If it doesn't see it, your hard drive has likely crashed. You will have to replace it, install a new copy of the operating system, and likely have lost all your data and documents. This is where I would start.

It is possible that Cd Rom drive is not functioning correctly. Do you have a second system you can test the Cd on to verify if it is the CD or your CD Rom drive that is bad.

If this doesn't resolve the issue I have 2 other ideas. :
1. have you run out of disk space? Go to My Computer and check. If you are under 1 GB of free space, try doing a clean up of your system with Disk Cleanup. To open Disk Cleanup click Start, point to All Programs, point to Accessories, point to System Tools, and then click Disk Cleanup.

2. Windows is corrupted and you need to try either a repair install or a fresh install.
To repair windows corrupt files you need to have a system utility software RegInOut

Two possible things are wrong either your hard drive has gone or your system has corrupted. Put your instal or system disk in start it up holding down the c key. Once it has started check that the hard drive exists by go to the menu bar and selecting the disk utility. If the hard drive shows it means that it is okay run the disk utility check drive and then run the repair permissions. Then try restarting, if it works then you are back up and running again. If the drive shows up and you restart and the same thing shows up with the grey screen, you will need to reinstal your system. You do this by starting up with the instal disk holding down the c key and run the instal script. To keep your hard drive contents your will MUST use the preserve users instal.

If your hard drive does not show up the hard drive is probably a gonner and you will have to purchase a new hard drive and instal a fresh system.

Hope this helps

It sounds like your system has corrupted. Put your instal disk in. Start your mac up and hold down the c key. Once it has started check that the hard drive exists by go to the menu bar and selecting the disk utility. If the hard drive shows it means that it is okay. Then run the disk utility check drive and then run the repair permissions. You can then try restarting, if it works then you are back up and running again. If it does not you will need to reinstal your system. You do this by starting up with the instal disk holding down the c key and run the instal script. To keep your hard drive contents you MUST use the preserve users instal which will come up as an option. Do not reformat the hard drive as this will wipe all your information.

If you have been running time machine as your backup operation you could instal a totally clean system and then select the time machine backup once the new system has been laid down using the migration utility in the utilities folder within the applications folder.

If your hard drive does not show up the hard drive is probably a goner and you will have to purchase a new hard drive and instal a fresh system.

Hope this helps

Two possible things are wrong either your hard drive has gone or your system has corrupted. Put your instal disk in start it up holding down the c key. Once it has started check that the hard drive exists by go to the menu bar and selecting the disk utility. If the hard drive shows it means that it is okay run the disk utility check drive and then run the repair permissions. Then try restarting, if it works then you are back up and running again. If the drive shows up and you restart and the same thing shows up with the grey screen, you will need to reinstal your system. You do this by starting up with the instal disk holding down the c key and run the instal script. To keep your hard drive contents your will MUST use the preserve users instal.

If your hard drive does not show up the hard drive is probably a gonner and you will have to purchase a new hard drive and instal a fresh system.

Hope this helps

The flashing question mark, indicates that the system cannot see the operating system.
Check for a failing hard drive
Trying booting from the Mac OS X install disc. insert the Mac OS X install disc. press the start button, while holding down the "C" key on the keyboard
Once you are running from the disc. go to Disk Utilities select the hard drive click the "repair permissions" button at the bottom.
If you get any red errors listed or it doesn't seem to finish repairing the permissions you have a failing hard drive and it will need to be replaced.
If this process finishes without any issues you will have to reinstall your operating system.

Two possible things are wrong either your hard drive has gone or your system has corrupted. Put your instal disk in start it up holding down the c key. Once it has started check that the hard drive exists by go to the menu bar and selecting the disk utility. If the hard drive shows it means that it is okay run the disk utility check drive and then run the repair permissions. Then try restarting, if it works then you are back up and running again. If the drive shows up and you restart and the same thing shows up with the grey screen, you will need to reinstal your system. You do this by starting up with the instal disk holding down the c key and run the instal script. To keep your hard drive contents your will need to use the preserve users instal.

If your hard drive does not show up the hard drive is probably a gonner and you will have to purchase a new hard drive and instal a fresh system.

Hope this helps

This means that operating system is corrupted, missing or faulty hard drive.
Boot from MacOSX install cd and check disk with disk utility or try reinstall macosx.
If that not gonna help then youll need to buy new hard drive and replace it.
To access hard drive you need to remove just 3 screws under battery.

The hard drive is probably on it's way out. You can get and run Disk Warrior and you could repair permissions and such but the hard drive is probably on it's way to the grave.

A couple things though. It isn't enough to just put the disk in, you need to hold down "c" while the computer starts for it to try to run off your disk. You can then try to repair permissions and fix the disk from the installation program that starts. When the Install OS X screen comes up (looks like a desktop but with the big dialog box in the middle) click on Utilities at the top and then on Disk Utility. HERE IS APPLE'S SITE for you to read about how to try to repair your disk. I've found that this sometimes works and may help it work enough for you to get your files off, but may not.

Another method would be to get another Mac, and hook the two together with a firewire to transfer your files, then reinstall OS X in your ailing computer. Go HERE to read about this technique.