Why doesn't my Samsung Galaxy Tab(GT-P1000N) connect to the WIFI

Please help me. Just a few days ago, my Tab could connect to the wifi perfectly fine but since yesterday,I couldn't connect to the wifi. When I go to the settings,it says it is connected but I cannot use it still. I have looked for many solutions yet they all say the same thing,reset it to factory settings,on the tab and off it,turn on the wifi and off it but still I cannot use it. It is very frustrating because I have reset my tab to factory settings and all of my apps and things I downloaded are gone and I cannot use it. Please help me if you know how to fix this. I can't take it to the Samsung center because the tab was given to me and I didn't buy it myself. I have also called to my wifi's modem technical help and they asked me to change my SSID and password but I changed my modem last week.Please it is very URGENT!!!! Also my other tab is also a samsung one but it also has the same problems. PLEASE HELP!!!