wifi connection lost

Hi,

I am connected through a wi fi router, which is connected to a adsl modem.
More and more regularly, I lose my connection. When I check the available
networks, I find my wifi router with 'excellent' reception.

So, I try to do a 'repair' but the process keeps blocking at 'Connecting to
the network'. After 10 secs, I got the message that it could not connect.

Then I have to go to the router and modem and switch both off then on again,
do a 'repair' and it works again.

Another weird thing is that sometimes my computer stays on for 1 hour when I
am away, but my connection keeps alive. When I use it for some time, then the
connection drops.

Is this malware? I have Antivir Avira and have run SpyDoctor which found no
big problem...

Can a mobile phone too close to the router interfere with it? But why does
the repair not work then?

Any hint would be appreciated.
Duxxyy.