Wi-Fi not connecting on my Lenovo g570?

You need to state more information. So what your going to do lacking information. Is go through the questions and follow them accordingly.
1: Does you computer detect the network you want to connect to?
-Yes- Then look on your computers keyboard at the function keys probably f12 there should be an antenna that looks like it is broadcasting the key may vary!
2:Does it have a light on it?
-Yes-
Is it orange?
-Yes-
Press Fn and the F key that is specific to your laptop
Did the light turn white?
-Yes-
Try reconnecting to the network now!