There are several possibilities.
- Your Hardware is faulty
- Remove or disable the Hardware and try with an other working one from a friend/neighbour
- Your environment is very noisy, then you can see it:
- Install "wavemon" (sudo apt-get install wavemon)
- start it: sudo wavemon
- press F2 to see the signal strength
- press F3 to see the other networks in your environment
- with ALT + Q you can quit the program
Interpretation of the seen data (here as example):
HomeWifi 00:00:00:00:00:00 100%, -36 dBm, ch 6, 2437 MHz 8 sta, Radio Measure
FRITZ!Box 7490 AA:AA:AA:AA:AA:AA 40%, -82 dBm, ch 1, 2412 MHz 5 sta, 11% chan, Radio Measure
<hidden ESSID> BB:BB:BB:BB:BB:BB 39%, -83 dBm, ch 1, 2412 MHz 3 sta, 7% chan
If the dB value is -36dB, then the received-signal power is better that -82dB. (should be clear)
If there are a low number of other router using the same channel as you, this is better.
There are other noise-creators which can not be seen during this scan. To example a microwave oven is creating 1000 Watt of power in the area of 2.4GHz and your router can only create 0.1Watt of power. The housing of a microwave-oven is not perfectly sealed.
An other possibility to scan the wifi-network is the command:
$ nmcli device wifi list