Wireless internet issues

Bought a new router (Linksys) a few months ago. It seems to work OK. Not great, but ok, considering the number of wireless devices we have (we can't signal in the back of our upstairs bedroom - where the bed is). When I changed routers we lost the ability print from our ipads to the printer. We can still print from our iphones. If I view our router and its connections the printer is not listed.
This week my wife bought a wireless extender. I'm trying to hook it up but I can't find our network. It's not showing up on any of our devices (desktop, phones, kindles, ipads).
It's there. Somewhere ... We all have connections, but I can't find it to connect the extender. (I tried disconnecting the firewall, but that didn't work). When you view wireless connections there's nothing showing up.
Now, when I fiddle with the HP printer, trying to connect it to our system, it connects - AND the network extender also finds our system, But only briefly. They both disconnect from our wireless system after about two minutes.
Any idea why?
Any idea where the issue is; printer? router?

 

Maybe try this (from How to Set Up a Linksys Router with Mac OS X | Garrick van Buren

Here’s the steps I took to setup a Linksys Router with Mac OS X

1. Peel off the sticker on the back of the router.
2. Plug in the router’s power cord.
3. Connect the router to your modem via the supplied Ethernet cord and the port marked ‘Internet’.
4. Connect the router to your Mac via Ethernet.
5. Open up the ‘Network’ panel in the Mac’s System Preferences and plug-in the following specs:
   IP Address: 192.168.1.5
   Subnet Mask: 255.255.255.0
   Router: 192.168.1.1
   
   
6. After applying the settings, open a browser to http://192.168.1.1 using the password 'admin'

 

Pretty sure I have the router set up correctly. I was thinking I had put on safeguards to hide our network. That might be true, but I can't find anywhere to check that.

 

Maybe check it on the router page?
Linksys Official Support - How to access the router’s web-based setup page

 

Did you try rebooting?