White (bootup) screen with the gray apple and spinning wheel?

It’s probably the 10.5.3 update that’s to blame.

(I’ve posted these answers before, here )

Try the following, nicked from Here

Clear the PRAM Reboot your computer while holding down the command-option-p-r keys simultaneously. Don’t let up until you have heard the startup chime three or four times.

Reset Open Firmware. This is a step for G3, G4, and G5 Macs only. If you have an Intel Mac, you should Zap the PRAM (see previous point).
Reboot your computer while holding down the command-option-o-f keys simultaneously. At the prompt, type
reset-nvram and hit the Return key, then type
reset-all and hit the Return key again. Your computer will reboot.

* Note that these commands are correct for New World machines, those with colored plastics (iMacs, Blue and White PowerMac G3) and newer. Old World machines (G3/233 All-in-one, beige G3, etc.) are slightly different—just type the reset-all command.

File System Check. This can be done in several ways, including
1. Boot to single user mode by holding down command-s during the boot process, then at the prompt typing
fsck -y and hitting the Return key. Continue to run fsck -y until no errors are found. (Note: if your hard drive is journalled, you will need to run fsck -yf. Attempting to run fsck -y will result in a message reminding you of this. Thanks to Petroffski.) Then type
shutdown -r now and hit the Return key to reboot.
2. Boot to a full OS X Install CD. From the Installer menu, select Disk Utility. Select your hard drive boot partition whose file system you wish to check, click on the First Aid tab, and click the “Repair Disk” button.
3. Boot to a third party disk utility CD and run the file system check offered therein. At this time, I can recommend DiskWarrior http://alsoft.com and Drive 10 or Tech Tool Pro 4 http://micromat.com . The third party disk utilities generally do a better and more complete job than the first two options and have been known to rescue drives that are inaccessible.

Reset PMU. Software PMU reset is ONLY for Apple portables, not desktop computers. The procedure is specific to each machine, so I can’t give a synopsis here. Instead, check Apple’s Knowledgebase article for resetting PMU on iBooks and PowerBooks and Apple’s Knowledgebase article for resetting PMU on MacBooks and MacBook Pros. This does roughly the same thing that pressing the PMU button or CUDA switch does for desktop Macs.

Zapping PRAM didn’t work. Did the File System Check (fsck -yf). Then did a shutdown -r now. Same issue.

I had this before after an OS X update, I just wish I could remember what I did!

There’s some chat on the same problem here .

One of the posts from here says:

The only thing you can do now is to get the mac os x dvd and reinstall the entire os. You do not need to format, just select the archive and install option. It will replaces all system files and retain all your personal files. All previous system files will be copy to a folder named “previous system”. After the reinstall process, update the 10.5.3 patch. Everything will work fine.

That sounds like an option, as it will retain files and settings?

More here and here .

I think @benseven has the only real solution; try an archive and install. Good luck.

Yeah. Macs never crash right? :-)

Okay, I will do the archive install.

what i ususaly do when customers have this update problem…find another mac, link them with firewire, then target disk the patient, throw on the combo update (downloadable through the apple site) and tadaa!