why do i have to leave the dsl modem on for 10 days?

usually, the soft ware that is installed into your computer from thier disks needs to be updated.

The updates are done automatically while you are online

This would be my guess..

here is what i found online.

In order to provide you with the best possible connectivity, your DSL circuit must "train" for at
least 10 days when first activated. During this period you must leave the DSL modem plugged
turned on and connected at all times. You do not need to leave your computer turned on during
this period- just the DSL modem. For best results, please plug in your DSL modem and turn it
the day before your scheduled installation date, and leave it turned on for at least 10 days.

dsl modem
just recently came back from a five week vacation .
before leaving i shut the system down and completely disconnected the system ... big mistake !!!
for several days i could not connect and when i phoned the help-line i received an automated message : "system is down ,,, we are working to re-connect".
i finally got fed up and managed to reach some other department at the server (the help line replayed the same message over-and-over-again , just couldn't reach them ).
it turned out that i had lost the internal settings and it took about 1/2 hour on the phone to get the settings back ... not much fun!
i'm never going to bring the system down completely .
hbg

sounds like your problem was with the isp not u powering down.

Simply just needed to state Now i am happy that i stumbled onto your page.

this is the DSL sync phase of setting up your connection, it warrants distance from the DSLAM and other interferences that arise from electronics cohabiting the infrastructure.