Internet Connection via WLAN

[GoRo]

Hi, I have a problem.

When I connect to the internet via WLAN it works fine, I use a DNS connection to the server. I can surf with no problems but as soon as I use a download manager (I tried 5 diffrent ones) it dissconnect my network connection and 1 sec later connects again but then the internet entirely dies. I need to reboot my pc before I can surf again, sometimes I can download for about 30 min without any hassles but other times as quick as 10 sec. Can anybody please help me.

A thanks in advance!!!