Try the long way:
Control Panel => Add Hardware => Follow all the instructions shown in the wizard.
If this doesn't help, come back to us.

Thanks for your answer

I tried that add hardware thing but it did not detect my modem when i did I tried to detect it automaticly, and I could not find it when I tried to choose it myself. Is there something i can do?

Did the modem come with an instalation CD?
Is it a plain modem that connects via a (Blue) USB cable? Or is it a Modem inbuilt into a router?

I don't rember what it came with because I have it since a long time, but I have an Internet setup CD (that had no effect when I reinstalled it)

My modem is inbuilt into a router

Thanks for your help

Have you tried connecting via an ethernet (RJ45) cable?
Either find one that you used, or buy one (very cheap seeing as every one has gone wireless crazy) then connect one side to the router and the other to the back of your machine if it has the correct port (they normally have a green and yellow LED on the top of the port).
Try this and you should get an internet connection straight away.
Going through an ethernet cable should wor for games.

I already use an ethernet cable. I tried pluging it directly for my modem to my computer, instead of passing by my router, but nothing changed.

Thanks a lot for your support

Is your router wireless at all?
If so you could try and get a wireless connection just to see if the router is at fault. This problem seems to be linked to the modem & router hardware.
Also what game(s) are you trying to play?

Yes my modem can do wireless, but I dont think hes the problem because my father can connect wirelessly on the internet with his laptop. I don't know how my computer could receive wireless internet tough.

For the games, nothing works: I tried to play Medieval 2 Total War, Age of Empires 3, World of Warcraft, Guild Wars, F.E.A.R, etc. What is weird is that I used to be able to play WoW and Guild Wars, but I stopped for a year and now I can't get in the game.

Oh, by the way, I tried Remote assistance to allow a friend help me from his computer, but it did not work, but I remember having used it not too long ago.

Thanks Serunson

Your computer could recieve the wireless signal if you bought either; a PCI wireless expansion card, or a wireless USB stick. The latter option is the cheapest and most effective. Seeing as it looks like a normal USB memory stick but does wireless connection instead of saving your data. You can also move it around the various USB ports on your computer. They vary in price so shop around for the best deal. Using wireless in games is fine but you do tend to get short periods where your connection may lag for a second or you get a very high ping for a short amount of time (split seconds nothing like minutes). This may be a future option for you. Also just check in the game itself that you have selected the correct Network options, normally under a section called Connection in the options menu, in most games.