download speed ( and bars on lower left corner ) go to zero
 

Sometimes i download a mpg file of 700 mb, which starts at 20-40 kbps. i dont know why , but some downloads with speed t3 or higher come fast at 140 kbps - ( my max speed on my computer ) but some downlaods of the same t3 or higher speed dont go above 20-40 kbps ,

Any way, the point is that if i leave my computer for over 4 hours, 2 ( sometimes ) or 3 ( mostly ) green bars on the lower left all turn red, and the downloading speed falls to 3 - 4 kbps if not 0.

if i shut down limewire and restart the oncomplete download, it resumes at peed of 20 - 40 kbps. Why does this happen, and how do i rectify it

You may want to try FrostWire. I works great for me and you don't have to pay for 'turbo-charged connection'.