cannot wifi sync again n again

I tried itunes wifi sync, just to have a check and it worked.

And later on again I tried to connect to itunes ( wifi ) but my iphone was not reflecting on the itunes.

I tried again n again like relaunching the itunes, connecting and disconnecting wifi on my iphone it just didn't work.

I cannot restart my system ( windows 7 ) again n again cos it worked after restarting.

Any solutions....