Here is a weird one...anyone help...?

I use a SpeedStream DSL modem for my high-speed internet access. Most of the time all is fine....However...every so often after I disconnect from the internet (I prefer NOT to have a continual connection) and try to connect later, I would seem that my computer has "lost" its connection to the DSL modem...I have tried exiting all running programs (including zone alarm and visus scanner) but not no avail....even tried uninstalling network card and re-installing it, as well as turning the DSL modem off and then on good. Only thing that will work is a complete restart of XP Pro...then all is fine.

Anyone know what is going on here?