The mac/Ip reservation will not help if it is a DNS issue. If it's a DNS issue, i believe the other devices wouldn't have worked either. Grab a screenshot of the WIFI settings page on your tab when you think it is supposed to be connected but Internet is not working and we can take it from there. When you tap on the SSID that you are supposed to connect to, it shows status/Signal strength/Logins failed etc. which is what you'll have to look at. Could be a software issue or a hardware issue in the worst case. if nothing works, you can try forgetting the SSID and reconnect again. If that doesn't work too, try a factory reset for the tab as last resort. Edit: I guess you meant to say DHCP issue and mentioned DNS instread. I still suspect something else is wrong.