Wifi Disappearing Refusing Authentication From Multiple Devices

The original network had a Zylex router, Netgear Switch. There was 2 pc's, one XP and Win 7. There is also 3 tills connected too. There is VPN network connected too. This emits a wireless signal to connect to a scanning gun and is also used to administrate the entire network. I was told by the Administrator of that network that it shouldn't interfere with the wifi network.

The job I was requested to do was to install 3 new wall plates as the Win 7 pc was using a Belkin wireless adapter. There was 2 put inside the office where the XP and Win7 pc's are located. The 3rd was just outside the office.

Now all the ethernet connections work 100%. The wifi is another story though. It will show up in the connect too, when you try connect it will disappear/no response from AP/connect then disappear, these are random too. No order to when each is error is displayed. Even when I put in another router the exact same issues happen.

I have tried to connect to both routers wifi when it wasn't plugged into the switch. Just the router's turned on with no cables plugged in separately of course, no joy same issue with both.