answer: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.