HI Jörgen and welcome to TSF !
Do you have both ADSL and dial-up at your place ? When you try to connect with the dial-up connection do you see the dial-up connection prompt and do you hear the modem dial the number ? If you only use ADSL at your place then go to control panel => network and internet connections => internet options => connections and delete anything you see under dial-up settings (if there was a dial-up connection there make sure you have the phone number, login and password written down somewhere).
Check the device status of your dial-up modem and network adapter in the device manager : start => run => devmgmt.msc. Double-click the device to see its status.
Go to control panel => network and internet connections => network connections. Right-click your network adapter => properties. In the general tab check that the following are installed and ticked :
- Client for Microsoft Networks
- File and Printer Sharing for Microsoft Networks
- QoS Packet Scheduler
- Internet Protocol (TCP/IP )
Highlight Internet Protocol and click properties. Check that both settings there are set on obtain ... automatically.
Right-click the network icon in the system tray and click repair (here's a
guide from MS).
Go to start => run and type cmd. In the dos command prompt type ipconfig /all. Right-click the window, click select all then press enter. Right-click => paste that information here.