Weird speed limiting problem

[urinal]

I have a 6mbit comcast cable connection. On one of my computers I get the full 6mbit speed, on the other it maxes out at 270k/s. This happened very recently, both computers used to be able to download at the max. Any ideas as to what might have happened? I don't have any bandwidth limiter installed. Thanks.

Also, I can download multiple things at the same time that added together equal 6mbit. I am thouroughly confused.