Slow connection speed can have many causes.  The telphone line, In house (inside the house) wiring, a cordless phone in the house interferring, a regular voice phone or answering machine, bad interconnect cable between the modem and the telephone wall jack and finally the ISP's modems. 

Unfortunately there is not "one thing" that will cause that.  You will have to play "detective" and try and isolate or find out where or what is causing it.

Yes like was mentioned you need to do some detective work as connection speed issues can be involved.  I suggest starting with the simplest things first like disconnecting everything that is connected to the telephone lines like fax machines and answering machines.

I suggest that you start with a quality made modem.

Have the telephone company check the lines for noise.

Update the modem drivers and set the modems string settings.

Update the firmware for the modem but use caution here as modem damage may result if you make a boo boo.

how to get modem drivers and check or set string settings?thanks for the 2 replys