to commonly asked questions.

My airport network is having problems.

The devices which you installed to boost my wi`fi i n the house have yellow lights on and service is weak downstairs from office.I un plugged the little black box but only two green lights reappeared.What must I do?

A couple of things at play here. 1st, the yellow flashing is either being caused by the presence of an update available or it could mean there's a problem with the network setup. Since you're experiencing problems with the signal strength it seems likely that the later is the cause.
Open airport utility and see if you can run any updates (denoted by red circles). After any updates are run now take an inventory of the devices present on the network grid. Screen Shot 2017-01-16 at 11.57.37 PM
As in the example above, if you see one device showing a yellow triangle, then that device has somehow fallen off the network. Check the power to that device first. Secondly you may need to hold the reset button on the back for approximately 5 seconds until the yellow light flashes rapidly then use airport utility to re-add the device back on to the network. Airport Utility does a very good job of making that process very easy to do.
This image is a theme.plist hack