My iMac won't stay connected to the internet, even though all other computers in my house stay connected

Question

My iMac won't stay connected to the internet, even though all other computers in my house stay connected, and its connection is set up the same way my fiance's macbook is (his macbook is about three years older than my iMac). Every time my computer goes into sleep mode and I come back (even if it's mere seconds after giving the black screen) I have no internet connection. I discovered a workaround for it some time ago, but now that is working less and less, and now my computer randomly disconnects WHILE I'm actively using the internet. Just a few minutes ago, the connection refused to come back until I restarted my computer, even though once again all other computers in the house were connected. The workaround I discovered before and which doesn't work as reliably now, is to click opne Airport at the top right of the screen, click "Open Network Preferences," then click "Assist me," then click "Diagnostics," and wait for everything to turn green again, signalling a connection.

Answer 1

Let's check the quality of your connection since signal strength alone does not insure a good connection. The "bars" that you see at the top of the iMac screen are there pretty much for show.
Hold down the option key on the iMac while you click on the Apple icon at the upper left corner of your screen and select System Profiler
Look down the list of items at the left of the window until you find the setting for Network, then click on AirPort.
In the window to the right, look for any listings of your wireless network name. You may possibly see two listings for the wireless network name.
We need for you to list the information that you see for Signal / Noise.  These will be negative numbers. Post back with your findings and we will continue.
In the meantime, please move any cordless phones that you have or any other electronic devices that are near the iMac as far away as possible from the iMac.
If the iMac is located in a corner or an enclosed area, give it as much room as possible since the wireless antenna is on the back of the iMac and it needs to be able to "see" the room.
Anything that you can do to minimize the number of obstructions like walls or furniture etc between the iMac and the wireless router will help the cause as well.