I just built a new PC, and everything on it works wonderfully. It's just that when I play games online, that I have a horrible ping. Well, I only really play one game online, TF2.
With my last computer I was getting a ping of 15-20 on local servers, now I'm lucky if I get a ping of under 120, I have a cable connection, and everything seems normal. The only other thing beside the ping that I can think of is that I moved the cable modem from one cable outlet to another.
Its possible when you moved your cable modem that you picked a line that has splitters in it before the cable modem. Cable modems should be on their own line and directly off the first splitter. Any other splitters can degrade signal strength and lead to problems.
If you can trace down where that line runs and connect it to the first splitter inside the house.