|I would suggest to use a Live CD and check, whether the problem persists.|
You may use a Linux Live CD like Knoppix for testing.
For testing with Knoppix, connect the machine by wire. So Knoppix will find the network card and you are able to access the internet with it.
If the machine is booted up with Knoppix and you got no problem, you're dealing with a virus or trojan on the windows system.
If the problem perists, your network card may be corrupt.
But, as you mentioned above, it doesn't matter, whether you are connected by wire or wirelessly.
Does wireless connection mean, you pulled the cable out of the network card? (It should)
The original poster should always write the last response !!!
Let us know, if the problem is solved !!!