[ubuntu] wireless network problem

my problem is that my wireless network card stop working suddenly ,,, when i am coecting normaly it just stop and shut down i discoect automatically from wifi and i when i try to coect again i doin't find it i don't find any wifi network its just like someone shut down all the routers ,, and after a while i reccoect automatically and all the wifi network shown again ,, it keeps doing this at least 5 times every hour what is the problem plz can any one help me what shall i do ?? :/