my airport express no longer extend my network

Thanks, but unfortunately you did not tell us about any troubleshooting steps that you may have already performed. (We don't want to waste your time asking you to do things that you have already done.)

But if you have not already done so, the first basic troubleshooting steps that you would want to perform would be......

Power off the Time Capsule

Power off each AirPort Express

Wait a minute

Power up the Time Capsule and let it run for a few minutes

Then, power up one AirPort Express and check to see if it is working correctly

Then, power up the other AirPort Express and check that device

If you need more help, we still need to know whether you are using AirPort Utility on a Mac or an iPhone / iPad, as we requested above. This will allow us to provide correct instructions for you.

We'll need some additional information from you. Things like......

What model of AirPort Express do you have?

What is the make and model number of your main WiFi router?

Are you using AiPort Utility on a Mac or an iPad?

What troubleshooting steps have you already performed?

Powering things off and then starting them up again will fix about half of all issues about half of the time, so it is always a good troubleshooting step to perform before you try other steps.