Machan follow these steps.After this simple tests u cn find out wherz the problem.......
01.Check ur phone line (May be thrz a loose connection or leak)
02.Check the splitter (Make a call when u r using ur connection.If ur connection speed is slowing down simultaneously the problem is in ur Splitter or the Micro-filter)
03.Check ur Micro-Filter (Micro filter is using for filte ur phone line band.U must use filter for optimal connection.If u r nt using MF,ur ADSL connection might get disconnecting continuously)
04.Check ur UPS if u r using UPS protected ADSL line.(Sumtimes if u r using those two built-in safety ports in ur UPS,they might nt work properly.Therefore connect phone line directly to the modem if the modem hs fusible protection)
05.Check ur modem cables(Cable with RJ11 Male port [Ethernet cable] or USB cable.Plz check ur cables.They might nt work properly if they r C grade or hand made cables)
06.Check ur modem firmware (If latest firmware is available.Download and install it)
07.Reset ur modem and re-config ur modem (Insert ur username,password and other settings)
08.TCP/IP connection (If ur modem configurations shows that DSL connection works without an interruption,logically we cn think that the problem is in ur TCP/IP)
09.Check ur Services (Sum tweaking softwares stop services to reduce memory usage bt those services might be interact with networking connections.U cn find services Control panel-> Administrtive Tools->Services)
If problem is still there,plz ask sumone to bring laptop and a ADSL modem.After that, connect ur modem into Laptop (or desktop) check if that problem happens again do it vice versa (ur PC and the other modem)
I hope these information would help u to solve ur problem.......
Cheers......!