Odd Wifi problem

I have a Macbook Pro 15" Late 2011 with Lion. I'm having lots of trouble with Air Video, StreamToMe etc. Sometimes the iPad 2 and iPhone 4s can see the Mac (connect) and sometimes they can't. This can change in a matter of minutes from working to not working and vice versa without me doind anything. The Wifi signal seems to be fine. Connections between AppleTV and iPhone and iPad seem to be fine too. But connections between Mac and the phone and pad and even AppleTV with AirFlick have huge problems.

Internet seems to work fine though. I am using the Mac right now.

Any suggestions?

Update #1

I tried plugging my Mac to the router with an ethernet cable but the same problem existed.

I also have turned off the firewall on my mac and the router which is a ZyXEL NBG4115.