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.
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.
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.