slow download speed caused by so, so many - many things. u need to be sure what u did to ur computer. it could be a malware attacking ur computer, trojans, worms, spyware, etc.
it could be the server that u r trying to download is busy or full, could not accept more connections.
it could be u r downloading from a location that is so far, far away thus making ur ping climbs up, up and away so high leading to reduced download speed.
let see what brink will bring to you here, and so for all other ppl below me who wanted to help you, thats all i could say.