MDK10-Why simetimes my ADSL (rp-pppoe) times out without connecting

Hi,
I have a Mandrake 10 (currently official, but upgrade from CE where the same
phenom occurred).
I use ADSL (rp-pppoe) to connect my PC (single, stand alone PC) to the
Internet and KDE 3.2.
I launch the connection by starting my PC (I don't leave it powered all the
time) and afterwards issueing 'adsl-start' (as root) from a terminal
window.
In about 80%, I get connected within 2 seconds.
In the rest of 20%, rp-pppoe times out, after about 1 minute, without
establishing a connection. Repeating the 'adsl-start' command (several
times) won't usually help. However, waiting about 30 minutes always help
and, after a wait, I usually get connected within 2 seconds.
I am using 750 Kb/Sec rate, and during ALL the time, my ADSL modem remains
synced as a rock.

How can I analyze, and solve, my connection problems?

TIA