Go to System > Preferences > Power Management. Check the setting next to When laptop lid is closed By default, It will be set to Suspend, which turns off most of your computer's parts except the memory (RAM) to save power, including the wireless card. Change it to Blank screen, then it won't do that.
Note that there are separate settings for when it's plugged into the wall and when it's on battery that you can select from the top. You'll need to change it for both.
Also, make sure that the Connect automatically box is checked in your wireless connection setting.
Go to System > Preferences > Power Management. Check the setting next to When laptop lid is closed By default, It will be set to
Suspend
, which turns off most of your computer's parts except the memory (RAM) to save power, including the wireless card. Change it to Blank screen, then it won't do that.Note that there are separate settings for when it's plugged into the wall and when it's on battery that you can select from the top. You'll need to change it for both. Also, make sure that the
Connect automatically
box is checked in your wireless connection setting.