My MacBook is a little over a year old running the latest update for Yosemite Version 10.10.5.
Thanks for the info. There are still some networking bugs in this version of Yosemite, so we are going to suggest a settings change on the MacBook.....if you have not already done this.....that might help the MacBook discover the AirPort Extreme.
If that does not help, you might be able to use an iPhone or iPad.....assuming that you have one....... for the setup of the AirPort Extreme, since the setup software on the iOS devices generally works better than the setup software on the Mac.
On your Mac......
Open System Preferences (gear icon on the dock)
Open Network
Click on WiFi on the left panel to highlight it
Click Advanced at the lower right of the window
Click the TCP/IP tab
Make sure that the setting for Configure iPv6 is set to Link Local Only
Click OK
Click Apply in the next window
Now click Ethernet on the left panel of the Network window to highlight it
Perform exactly the same steps as above
Restart the Mac
Perform a Factory Default Reset on the AirPort Extreme again, please.
Then, temporarily move the AirPort Extreme to the same room or close proximity to the Time Capsule
Click the WiFi icon at the top of the Mac's screen and look for a listing of New AirPort Base Station
Just below that, click directly on AirPort Extreme
When you click on AirPort Extreme......assuming that it now appears.....that will get the setup "wizard" up and running. The wizard will take a minute to suggest that the AirPort Extreme will be setup to extend the network that the Time Capsule is producing. The window will look similar to the illustration below, except that you will see your devices pictured.
Type in a short, simple device name that you want to call the AirPort Extreme. Mine is Extreme, for example
Click Next
The wizard will setup everything for you. When you see the message of Setup Complete, click Done.
Now move the AirPort Extreme to a point that is about half way between the Time Capsule and the area where you need more wireless coverage. In other words, if you need a better signal in an upstairs room that you normally use, locate the AirPort Extreme about half way between the Time Capsule and the upstairs room.
The more that you have line-of-sight between the Time Capsule and AirPort Extreme, the better the network will operate, and the faster the wireless speeds will be. Even with line-of-sight though, the potential speed of the entire wireless network will drop by about half. Chances are, the resulting speed might still be faster than your Internet connection, so you might not notice the slow down when using the Internet.
If you are copying files from one end of the network to the other, it will take about twice as long for the process to complete compared to having your Mac in the same room with the Time Capsule. That's just a nature of the beast with wireless. If the speed loss is significant to you , the only way to regain the speed will be to establish a permanent wired Ethernet cable connection between the Time Capsule and AirPort Extreme.
One of the upsides of doing this is that you can locate the AirPort Extreme exactly where it is needed, and you don't have to use a compromise location like you do when you try to wirelessly extend the network.
Please post back on your results.