iMac Airport problem

[Matetus]

I have a recurring problem with Airport on my iMac(Snow Leopard 10.6.8, Build 10K549), every 6 months or so a problem occurs in the same manner:
Stage 1:
Connection to home network(WPA2) drops every now and again(usually once every 2 days) and continues to do so for roughly 2 weeks
Stage 2:
Can't connect to home network, this usually lasts for a week
Stage 3:
Can't connect to any wifi network(WEP,WPA2...)

This is the 3rd time it's happening and it's to say the least, frustrating.
I tried erasing all known networks and restarting many times, but to no avail.
I usually format the entire HD and put a clean install of Snow Leopard and I'm fine for another 6 months, but it's irritating, every 6 months i have to put every work I have on hold for a day or so.

Does anyone have any clue how to fix this or has even heard about something like this?

 

[BrianBaughn]

What kind of router...and have you tried restarting the router?

 

[Matetus]

Thomson st780, but i don't think that the problem is with it, because i can access the wi-fi network without problems from my laptop(win 7)

 

[btbrossard]

I'd try rebooting the router when this happens to see if that helps.

Also - when this happens can you connect to the internet with an ethernet cable (if possible)?

 

[Matetus]

I'd try rebooting the router when this happens to see if that helps.

Also - when this happens can you connect to the internet with an ethernet cable (if possible)?

I tried rebooting it too, but, nothing :/
And it's not possible for me to connect using an ethernet cable.