atmost

I am using P 3 933 / MSI 6137 Mobo + 256 Mb Ram 40 Gb HDD and using Win XP PRO.Recently I purchased a D-LINK DFM 560ES 56 Kbps External Modem but whenever I connect to the Internet it says "Connected at 40 Kbps or atmost at 44 Kbps during latenights/earlymornings. All I want to know why is it...