windows slows down drastically when connected to the internet

I've installed windows 7 64bit on a brand new 500gb hard drive.
I've installed the basic software, i.e. antivirus and firewall.
I've ran and installed all windows updates.
The system runs beautifully until I connect to the internet.
As soon as I do this the whole system slows down to a snails pace.
Opening directories, starting software, browsing, everything.
once off the internet everything returns to normal.

Any pointers?

How are you connecting to the internet?

Wireless? Ethernet?

If wireless you may want to check you have updated wireless adapter drivers.

sorry, you are correct.
I did updates at my office using a wireless internet connection.
The client has a BB connection at his home.
I did not notice any major slow-down when using my wireless.
when the client connects thru ethernet, the whole system basically stalls.

In that case, you need to make sure your ethernet adapter has the right drivers and is set up correctly.

Please post the computer specs so that we can help further.

Thanks for your input.
I'll need a day or two to get the computer back.
I will try your suggestions.
I'll post the results.

Thank you.

You're very welcome.

We look forward to a positive outcome. :)