about any of what you've referred to, (do you have another thread on this?), but without any other knowledge of your system my first guess would be that the system is being "woken" by some activity on either the modem or network card.
Do you have a modem in the PC connected to a phone line?
Do you have a network interfact connected to a router that's on?
If so I susupect that somewhere in the BIOS you have a "Wake on LAN activity" enabled, or something similar.
Apologies if this doesn't help!