For some odd reason, I had issues initially connecting 2.4Ghz with my laptops. 5Ghz would connect fine, wired would be fine.
It took me turning on my XBOX to get the 2 laptops (LT's) to connect. Then the first time I turned off the XBOX, the LT's disconnected. Furry suggested unplugging the power plug to the back of the XBOX and so I did that, too. With some more rebooting of the router and my devices, 2.4Ghz became stable and has stayed that way.
So, don't give up, it's got some weird issues. I would suggest turning on every device you want to connect and then try configuring if configuring them with them all off didn't work.
Also, change the wifi channel from the stock channel 6 to another (use inSSIDer to determine traffic) and uncheck the box that says "Enable Auto Channel Scan".