problem with internet connection

[sowon]

hi I have Macbook Air since last year .It worked fine till few weeks when the computer is not recognizing my network .it shows other networks but not mine .I had to type it time after time.lately I re-installed system but the problem is still existing .sometimes the network is seen at once ..sometimes i need to restart the router and the pc..othertimes ..i am all lost..any explanation?and suggestions ?thank you.