I'm here again and frustrated.
The conection was fixed 5 hours ago, thanks to Eric. I went to sleep and when I woke up and started my Mac, the problem showed up again - could not connect to the wireless router and gets the error message "connection time out". I did the suggestion that worked earlier, but it did not.
Connection to the wireless router worked again when I restarted the modem, then restarted the router and then restarted my Mac. Then I turned off the Mac and after a few minutes, turned it back on and the problem comes back - could not connect to the wireless router and when I try to connect, I get the err
This issue did not show up until I upgraded to Mac OS X 10.8.3. It was working before when I was using 10.6.x.
I grow tired of this issue. Is there a solution to this? A friend of my suggest to reinstall Mac OS X 10.8.3. How do I do it when I purchased the item from the App Store? Another suggested to enable the Mac filter of the router.
Try going to System Preferences/Network and click the 'Assist Me' button on the bottom. You can run diagnostic tests or it will help you set up the WiFi again.
You can also try highlighting the WiFi in the left column and deleting it using the minus sign. Then hit the plus sign and add it back or you can use the Assistant under 'Assist Me' to set it up again.
To reinstall Mountain Lion, do a backup. One of the links above suggestion doing a clean reinstallation. Boot to your Recovery partition (holding down the Command and R keys while booting) or by holding down the option/alt key during restart. Select the Recovery Volume. For a clean reinstallation, use Disk Utility to erase the disk after noting the format (Mac OS Extended (Journaled)). If you want to try the reinstallation without erasing, you certainly can. Next reinstall Mountain Lion.
Send Apple feedback. They won't answer, but at least will know there is a problem. If enough people send feedback, it may get the problem solved sooner.
If you monitor the "More Like This" box (top right), other threads appear. Opening them usually displays other threads.