Having network problems :(

I recently started having network problems. Normally if I click on the WiFi icon in the menu bar it'll show a bunch of different WiFi networks to connect to, as well as mine.

But recently it has not been showing any of them, and it seems if my iMac goes to sleep and I wake it up it's disconnected from my WiFi and if I click on the icon in the menu bar no networks show up to connect to one, so I am forced to use an ethernet cord in order to connect to the internet.
Which is very annoying.

Anyone else have this issue or does anyone know how to fix this annoying issue?

MAC OS X 10.7.4

Any help would be appreciated

Thanks,
Jon

I too have the same issue, when my MBP goes to sleep it looses the wifi connection and sometimes I get an error stating that another device using this connection has the same IP address and I have to try and reconnect, without any success. I have to restart my system to get it to logon to the network. of course I am in Kuwait where the internet really sucks, but I still shouldn't have to restart to reconnect.

jppv sorry to ride on your post