Disconnect all devices from the computer then do the following:
Boot up from your Snow Leopard Install DVD while holding down the "c" key.
Select the language you wish to use, and then choose "Disk Utility" from the menu bar.
Your HD should appear in a panel on the left hand side of the window which opens. Select it and then click on the "repair disk" button in the right hand section of the window.
Once this process has been completed restart your computer and repair permissions directly from Disk Utility.
If Disk Utility is unable to complete the repair, you will need to use a stronger 3rd party utility like DiskWarrior, Techtool PRO (not Deluxe) or Drive Genius.
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If you are using your iMac wirelessly......
Try the basics first:
Change your router channel number. Most times this works & is all you have to do.
Disconnect & reconnect your modem. unplug it for about 10 seconds. Plug it back in. Do the same for Apple’s routers. Wait for everything to reboot.
System Preferences>Network
Click the Assist Me button.
In the next window that pops up, click the Diagnostic button & do the necessary.
Research Knowledge Base for network problems that pertain to the OS that is currently installed on your computer. See these basic networking KB Articles: http://support.apple.com/kb/HT1401 AirPort troubleshooting guide
http://support.apple.com/kb/HT4628 Wi-Fi: How to troubleshoot Wi-Fi connectivity
http://support.apple.com/kb/HT2712 Using network locations in Mac OS X
Manually provided DNS server addresses are higher priority than DHCP's
http://support.apple.com/kb/HT1714 Solutions for connecting to the Internet, setting up a small network, and troubleshooting
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What to do when you can't connect to the Internet
Also, run the Airport Utility app which is located inside the Utilities folder.
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If using a Linksys router, contact LinkSys Customer Support and/or post in their forums.
If using Apple's Airport, please re-post over in one of the AirPort Forums.
