Computer is caching an old version of a webpage - have tried everything!

Question

I would ask Applecare (which I have) about this problem, except that they are only open "business hours"!!!!!!!
I created a new website for my sailing club with a new host. On Monday, I had our old host and registrar point our domain to the new host. 48 hours later everyone but me could see the new website.
96 hours after the repointing, I still see the old site on Safari, Firefox and Chrome. I have refreshed, deleted caches and restarted the computer numerous times. Have repaired permissions. Have turned off Open DNS. Have used Onyx to delete all internet cache files. Have spoken to the new host and my ISP and neither says it is their problem. (I have not asked the old host to delete the site from their server.) My ISP says it is not their problem because my iPad, using the same wifi router as my computer, can see the new site.
Why, oh why, can I not see my new website on my computer???
Does anyone have any tips?
Am going a little crazy here!!

Answer 1

You, or someone using your computer, may have hacked the system to redirect queries to certain servers. The file modified is /etc/hosts.
The easiest way to fix the hosts file is to restore it from a backup that predates the modification, or to copy the unmodified file from another Mac. If you can't do that, then do as below. Please read this whole message before doing anything.
Back up all data. This is a simple procedure, but if you don't follow the instructions exactly, you could be left with an unbootable system. In that case, you'll have to restore from a backup or reinstall OS X.
If you have more than one user account, you must be logged in as an administrator. I've tested these instructions only with the Safari web browser. If you use another browser, they may not work as described.
Triple-click anywhere in the line below on this page to select it:
open -e /etc/hosts
Copy the selected text to the Clipboard by pressing the key combination command-C.
Launch the built-in Terminal application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid.
Paste into the Terminal window (command-V). A TextEdit window should open. At the top of the window, you should see this:
# Host Database
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
127.0.0.1                              localhost
255.255.255.255          broadcasthost
::1                                        localhost
fe80::1%lo0                    localhost
Below that, you may see some other lines. There should be nothing above the first line "##". If you have any doubt about that, STOP and ask for guidance. Make sure you scroll all the way to the bottom. Scroll bars are hidden by default until you actually start scrolling, so you may not realize that you’re not seeing the whole document.
If the contents of the TextEdit window are as described, close it, then enter the following command in the Terminal window in the same way as before (by copy and paste):
sudo sed -i~ '11,$d' /etc/hosts
This time, you'll be prompted for your login password, which won't be displayed when you type it. If you don’t have a login password, you’ll need to set one before you can run the command. You may get a one-time warning to be careful. Confirm. Quit Terminal.
If you see a message that your username "is not in the sudoers file," then you're not logged in as an administrator. Log in as one and start over.
That will fix the hosts file. There is now a copy of the old hosts file with the name "hosts~" in the same folder as "hosts". You can delete the copy if you wish. Don't delete the file named "hosts".