Why does my internet constantly freeze since I hooked up Airport Extreme?

Question

I purchased an Airport Extreme for Wi-Fi and to back up my MacBook files.  I had it hooked up for about 2 week now and since then, it seems our internet is constantly freezing.  Sometimes its just once other times it happens every few minutes.  We stream video often and it has been getting stuck all the time.   It seems to be the worst in the early morning and around 8:30 at night.
I'm not network savvy but will try to secribe how it is hooked up.  I have the airport connected via a modem (not wifi) with Ethernet.  The internet is DSL.  There is also a security camera connected to a D-Link router that I plugged into the Airport.  There's also some kind of internet feed for our PV system that I connected directly into the Airport too. 
We have Apple TV, 1 Macbook, 2 iPads, 2 iPhones, 1 iTouch, 2 PCs, 1 Sam Sung phone.   There can be up to 3 devices streaming video at once.  I thought it had something to do with the D-Link camera but not sure.
We disconnected the Airport today and connected a Westtell router and so far no freezing.  I saw some posts about D-Link and Airport Extreme not being compatible but I'm not sure what that means.  If they are incompatible, does that mean I have to choose to use the Airport and get rid of the security camera or vice versa??
I'm frustrated because the Extreme was expensive and I'm wondering if I can ever get it working.

Answer 1

On your MacBook: Go to System Preferences > Network. Select Wi-Fi from the left column. Click the Advanced... button.
Under the Preferred Networks list, select every Wi-Fi network that appears and delete each one using the "–" (minus) button. Select the box "Remember networks this computer has joined" if it is not already selected.
OK then Apply.
Select your AirPort Extreme's wireless network in your Mac's Wi-Fi menu, and determine if that solves its connection problems.
Our alarm company set up the camera with the D-Link before we got the Ariport and we can't figure out how to hookup the camera to the Airport without the D-Link.
You may need to solicit the security company's help. Adding your Extreme to your network as a router constitutes a fundamental change in your network's design. If you are now using the Extreme as your router, the D-Link router should be reconfigured as a bridge. Depending on the nature of your security system, it may not be required at all, but your concern about the security camera requiring specific port forwarding settings is justified. Changing your router from the D-Link to the Extreme may require forwarding specific ports using AirPort Utility, otherwise your security camera's video may not be accessible from the Internet. This goes beyond any help I can provide, since your security system has requirements of its own.
Configuring the Extreme as a bridge is likely to solve the problem... but if the D-Link wireless router was sufficient, do you really need another access point? The reason I'm asking is this:
... I purchased an Airport Extreme for Wi-Fi and to back up my MacBook files. 
If you need a wireless backup device for Time Machine, a Time Capsule may be a better choice.