I'd check Device Manager to see if you have any entries with ? or ! next to them. If so, you need to download the necessary driver(s) from Gateway. I hope you ran the program to tell you of any compatibility problems before you did the upgrade, and I hope Gateway has the drivers you need.
My Gateway laptop MD7818u has been giving me fits. The dc plug was bad, had replaced. Worked normal til the solder came loose and plug fell into the laptop. So I taught myself how too do a teardown, no problem. I re-solder the plug and all was good, again. After a few weeks I installed windows 8.All was working great again for a few days then I noticed the charging Icon was not showing up when plugged in. The battery and charger are both new, but I understand new don't mean good. So my mom has a gateway lap with the same battery and charger, still no icon. Her charger didn't charge or help solve any questions of what is wrong. I can charge my battery on hers and mine works fine till it dies. So by chance I got another dc plug and replaced, still the same. So no Icon for battery charging and both chargers won't work on mine. My charger won't work on hers, Now I'm more confused. I have check all the settings and all is correct. Did I mess something else on the motherboard ?? I'm lost and hope this make sense too you all. Better stop there.