Safe Mode
<p>Starting up into Safe Mode does three things to simplify the startup and operation of your computer:</p>
<ul>
<li> It forces a directory check of the startup volume. <br /></li>
<li>It loads only required kernel extensions (some of the items in /System/Library/Extensions). <br /></li>
<li>In Mac OS X 10.3.9 or earlier, it runs only Apple-installed startup items (some of the items in /Library/StartupItems and /System/Library/StartupItems - and different than login items). <br /></li>
<li>Mac OS X 10.4/10.5 only: It disables all fonts other than those in /System/Library/Fonts. <br /></li>
<li>Mac OS X 10.4/10.5 only: It moves to the Trash all font caches normally stored in /Library/Caches/com.apple.ATS/(uid)/ , where (uid) is a user ID number such as 501. <br /></li>
<li>Mac OS X 10.4/10/5 only: It disables all startup items and any Login Items. <br /></li>
</ul>
<p> </p>
<p><strong>Start the machine in Safe Boot Mode</strong></p>
<p><strong></strong> To start up into Safe Mode (to "Safe Boot"), do this (10.2 or later):</p>
<ol>
<li>Be sure the computer is shut down.</li>
<li>Press the power button.</li>
<li>Immediately after you hear the startup tone, press and hold the Shift key. The Shift key should be held as soon as possible after the startup tone but not before.</li>
<li>Release the Shift key when you see the gray Apple and progress indicator (looks like a spinning gear).</li>
</ol><br />
<ul>
<li> During the startup in Mac OS X 10.2 through 10.3.9, you will see "Safe Boot" on the Mac OS X startup screen.</li>
<li>During the startup in Mac OS X 10.4 or later, you will see "Safe Boot" on the login window, which appears even if you normally log in automatically. <br /></li>
<li>To leave Safe Mode in any version of Mac OS X, restart the computer normally, without holding any keys during startup.</li>
<li>Certain Mac OS X features do not work when you are started up in Safe Mode. For example, you can't use DVD Player, capture video in iMovie, use an AirPort card, use audio input or output devices, or use an internal or external USB modem. <br /></li>
<li>Safe Boot will take longer than a normal boot. This is normal; among the things it's doing is a filesystem check (fsck). <br /></li>
</ul>
<p> </p>
<p>If this makes the problem disappear, then it is a problem with Extensions or StartupItems. And most likely, those would be 3rd party Extensions or StartupItems. Most of those are kept in /Library/Extensions/ and /Library/StartupItem/. Move those items to the desktop, and see if you can isolate which one was causing the trouble.</p>
<p>There are also some 3rd party extensions that are annoyingly installed in /System/Library/Extension/, however you must be very very careful mucking around in there, as almost all of those Extensions are supplied by Apple, and your machine will not function without them. Use common sense, and ask someone if you're not sure.</p>
<p> </p> <br />
