Help with troubleshooting speed. download is 1.6 mbps!!

Hi Guys, Need some troubleshooting help with my connection. My speed has decreased drastically beginning in early January, dropping from 27-31mbps to 1.6 mbps
Here is what I have done so far
I have power cycled my router, and I have swapped out ethernet cables to both my router and to my PC.
I have bypassed my router and, direct connected thru my modem . Oddly enough, this was even slower


I am running teamviewer so I can simultaneously check speed on my other win 7 PC (3 feet away) where my download speed is 30.1mbps

I have wirelss devises in the house that have good connection so process of elimination points to my PC. It would be nice if it just stopped working all together. It is the slow speed that confuses me.

Buy an ethernet card and be done with it or have I missed something?

Thanks in advance for your assist

Tami