Ann, I think there are two major possibilities, but they're both a little hard to explain and I'm not sure how to give you the instructions to fix them.
1) One possibility is that this has to do with timeouts of the "lease" or connection the modem gives the router. I had this issue with Yahoo/SBC DSL and a Netgear router. The router would mysteriously stop working after working for a minute or two, or else it would not work if the computer was asleep for a few hours and then restarted. In the router settings, the solution involved a setting which said something like "if I am idle for more than xxx minutes, give up my lease/connection." This setting also had a "keep me connected all the time" sort of option. When I switched to the latter option, my issue was resolved.
2) The other one is that some modems have the ability to operate in two modes. One is called bridging, and the other is usually called routing or something like that. The problem is that the router must be set up differently for the two modes, and sometimes one of the modes doesn't really work. This is an issue with DSL much more often than Cable modems (which is why I asked you for those details). You should have received some kind of username and password from Tele2. The easiest way to tell which config your router is set up for is that, if your router is set up for a bridging modem, then you have put your name and password into your router's config, and if it is set up for the other method, then you have not (and may have put it into the DSL modem).
If #2 is the culprit, then you have to follow two steps:
- You have to figure out which mode your modem is set up for, first, and make sure that your router is also set up for the same mode. If you can't find the instructions for accessing the modem, then plug a computer directly to the modem, open system preferences -> Network -> Ethernet adaptor -> TCP/IP and copy down the IP address under "Router" and then point a web browser to that IP address, and you should get the config screen for your modem in the browser.
- Once you know that your router is set up for the same mode as your modem, then if you are still having problems, set the modem to the other of the two modes and also re-configure the router accordingly.
Hope that helps? It's complicated, and we can help you through it piece by piece as you go.