erm...recently i got a problem for the past 1 month

i current using broadband 1500kps from singapore.

i experienced very slow connection but i was unable to solved it but some of times (example once in a week, the speed of the internet will be like normal wat shld be)

i tried doing reformat..but the connection is still very slow. i decide to change my modem..however it din works as well. so i borrowed one of my frenz laptop to try at my home.but the internet is still very slow. but when i bring the same laptop n same modem from my house to my frenz house.. it work perfectly fine..

wat is happening?
wat causes it?
any guys can help me solve?