My Iphone 4s has stopped connecting to wifi at all! Blue slider is not even visible to turn on!

My just over a year old iphone 4S stopped connecting to wifi. It started by not keeping the connection for very long. I would reset Network settings and that worked for a couple of weeks. Suddenly the actual blue slider bar won't even allow me to turn the wifi to "on" period!! I tried to erase and restore my phone but nothing. Had to manually install all my apps as iCloud won't connect as I need wifi! Help please!!!