I have had similar issues with my Aspire s3 391 as well. for me it was a two part fix.
Part one I found here on the Acer website. http://acer.custhelp.com/app/answers/detail/a_id/27675 Follow those intructions and see if that helps.
For the most part that solved it except sometimes when I was running on battery for a long time it was come back. This turned out to be a setting found deep in the power settings. Here is the menu path to get there, open your Charms bar and click settings, then click control panel. Now you want to click power options. (if you are in category view you will first need to click "hardware and sound" to get to power options) On the power options page there are two default plans Balanced and Power saver. The one you are using will be in BOLD text. Next to that will be a link to "Change plan settings" click that link. On that page there will be a link that says "Change advanced power options" click that and a small window will open. Scroll down the menu in that window until you get to "wireless adaptor settings" click the plus nest to that to expand it and a new options will apear below that says power saving mode. Click that plus to expand as well. Now you need to change the setting for both optins to maximum performance.
These tow steps combined seem to have fixed the problem for me. I am currently expirementing with the low power saving setting for on battery to see if it works as well and have not had any problem so far but it has only been one day.
I hope this helps you as it took me quite a while to find these two things myself and I know how frustrating it can be when your new computer is not working proerly.
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