I can´t get connected to wifi in acer aspire 300lci

The most common reason for lack of wi-fi is that the laptop maker put a hard-to see switch somewhere on the rim of the chassis. My Acer 3003lci has it disguised as an activity light on the front-center edge; if you acidentally press it, there's a light 'click', the orange light goes out, and the wi-fi device is turned off. Press it again, it's back on and takes a minute to find and reconnect to wi-fi. Others I've helped have HP laptops, where the switch is a slider with the tiniest blue pin-light to show whether it's on or off.

The 2nd most common reason is that Windows, in its infinite wisdom, thinks it can run the laptop's wi-fi device better than the device's firmware, and disables the device driver in favor of its own. If you tinker with the settings, you can fix this, but it requires much patience.