Wireless router help please!!!?

i have the linksys by cisco wrt400n router Simultaneous Dual-Band Wireless-N Router. It has a 5GHz wireless and a 2.4GHz wireless. Recently the 5GHz one stopped showing up on my ipod's wireless newtwork list and my sister's iPhone but the 2.4GHz one still shows up. I checked the settings for the 5GHZ and it says SSID Broadcast enabled. So why doesnt it show up? PLEASE HELP!!