ok let me explain
first of all,I assume u r not using a leased connection.
Like any major highway system, the Internet information highway has many roadways and interchanges, each with their own capacity and speed limit, and, like highways for cars, sometimes you get traffic delays. Just as you have to wait in a your car while other traffic goes through at a traffic light, data sent to your computer has to wait while other data passes through routers, the Internet equivalent of an intersection, on it's way to you.
You are more likely to run into slow Internet traffic during peak use hours than those times when fewer people are online, such as after 11 p.m. and before 7 a.m. When this page was being tested, I found that the results on my 2MB DSL line results varied from a consistent 1400>Kbps mid-morning and afternoon, all the way down to 64Kbps during evening peak-use hours.
if u need to run a speed test do it on off-peak times