ac750wifi range extender model 3110

You didn't give us much more than you have the EX3110 and you can't get it working. 

1. what router are you connecting it to? 

2. what firmware is on the extender?

3. are you setting it up using the installation assistant or using WPS?

4. where is it failing in the process?

As well as dealing with the questions from plemans, the manuals are always a good place to start.

Visit the support pages:

Support | NETGEAR

Feed in your model number and check the documentation for your hardware.

That page will also have any software, firmware and drivers for your device, if they exist.

Begin with the Quick Start/Installation Guide.

There may also be some helpful videos on what to do.

You may have done that already. I can't tell from your message.

I mention it because Netgear gave up on supplying paper manuals and CD versions some years ago and people sometimes miss the downloads.