PC gets choppy when running games and Internet speed gets slower

My computer is having problems. I have just upgraded to Windows 7, the new Mobo, a new RAM and CPU.
My drivers are all up-to-date and have done defragment and virus scans.
When I run games, it starts okay, but it eventually gets too choppy to play. Browsing the Internet also gets slower the longer I stay online, and some website buttons no longer work as they had before (e.g., clicking “reply” in a forum takes me at the top of the page).
I checked on Speedtest.net, and I have a ping of 75 ms, my upload speed is 0.75 Mbps, and download speed of 6.19 Mbps.
