This could be caused by a BIOS settign on your PC.
Most BIOS modules have an option for the Network port named something like
'Wake on LAN activity'.
If your broadband is connected to your router via a network cable, and this
option is switched on then any broadband activity may cause your P.C. to
either not shut down, or wake up again.
The only LAN related BIOS option is Onboard LAN (disabled/auto).It is set to
auto.
PC is stand alone . High speed modem plugged in pc in onboard LAN.
In XP configure LAN connection properties has "wake on magic packet" "wake