Problems with wifi connection

[breezy123]

i purchased my iphone used online, i have had it for about 3 weeks now, i do not no much about it, i am not electronicly retarded but i know nothing about my iphone. the wifi on it worked for the first 2 weeks but now its not working. it used to work in my home and at my school but now it wont even recognize any of the wifi connections around me. ive tried resetting the settings and even tried resetting the network settings but nothing has worked so far..any suggestions???