Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Tips to speed up Reboot and Start Up time on your Mac
If you noticed that your Mac is getting slower when booting or starting up,this could be a result of a few things: a large login item list, way too many windows being restored, the general hard disk speed or really slow external drive.Don’t panic though,most of these issues are very easy and quick to fix.Follow these tips and you’ll see your Mac starting up quicker than it did before.
1. Clear out login items
When you remove unnecessary login items –- you make it easier or Mac to boot,because it doesn’t have to do as many actions for computer to get ready to operate as it did before.This alone can make a significant difference.Login items can be helper daemons,menu bar items,or full blown apps.Remove everything you don’t need to automatically start or you don’t use often.Here’s how you do it:
1) Open “System Preferences” and click on “Users &- Groups”.
2) Click on the user account you regularly boot with,then click on the “Login Items” tab.
3) Select items from the list you do not need to launch on login and click the [-] minus button to remove them one by one.
2. Disable Window &- App restore
OS X Lion has the Window Restore feature, an addition that some people find to be a lifesaver and other are really annoyed with.The benefit to turning off Window Restore is you are going to have faster startup times because Mac OS X doesn’t have to resume the previous state:
1) Open “System Preferences” and click on “General”.
2) Uncheck the box next to “Restore windows when quitting and re-opening apps”
3. Disconnect unused external drives and devices
A lot of external hard drives are really slow.The best solution is to disconnect any unused external drives,because every time you reboot they have to spin up and be accessed again,which takes time.Also,eject any discs from the Mac that you are not going to use.As simple as it is –- this might shave 10-15 seconds off boot time.
4. Upgrade the hard disk to SSD
This solution might not be very practical for an average user,but upgrading the hard drive on a Mac from a traditional spinning disk to a Solid State Drive (SSD) will not only speed up boot times,but also improve system performance in general.SSD drives are getting cheaper these days and they are definitely worth those few bucks you spend on purchasing one.
One last tip –- it won’t help boot performance,but another option is to avoid rebooting or shutting down.Instead,use sleep.If you’re shutting your computer down when your system requires a significant update you’re going to experience a long waiting time when booting later on.