So you resetted PRAM, try doing the SMC reset as well.
After that this is what you can do, hopefully it will solve your problem. It solved mine.
Boot with your OSX restore disc, and go into Disk Utility. Select your OSX partition (not the HDD, but the actul partition), and repair the permission. I repaired it twice just in case.
Then repair your disk partition (don't bother with the "Verify Disk").
Reboot into your OSX partition. Hopefully this solves your problem.
I have had slightly longer bootup time (circa 3 seconds), and shutdown time (circa 8 secs) on my 13" mbp Intel SSD after the 10.5.8 update. Doing the above fixed my problem. Not only that, my bootup time improved by 4secs approx. and shutdown time improved by 2secs appox.
P.S. Just so all of you know, power cut can disrupt/corrupt system files. Another scenario whereby system files can be corrupted is by forced OS shutdown by hitting and holding the power button (which is what most of us do when the system hangs). If you often do a forced shutdown or if there's frequent power cut, your system files will get too corrupted to the point system bootup and shutdown will degrade.
In the event like this, repairing the partition (done via Disk Utility from the restore disk) will most likely solve your problem. If it doesn't, it probably means you have a dying hard drive. I've experienced this with my iMac as the power supply in my area is not stable, causing lotsa power cut.