IDEA:Auto-boot Up computer after power outage?

Scenario:
I have a computer with Asus M3A78-EM Mobo. Also I have the PC connected to a UPS (uninterrupted Power Supply) which can provide power backup for about 15 minutes. I have frequent power cuts; duration ranging from 10 minutes - 90 minutes 4 times a week; I run (want to) the PC non-Stop for days for downloading stuff & various other things.

The problem:

When power outage lasts more than 15 minutes, the UPS cannot hold it and so system powers down. I cannot power on the system unless I am physically present beside my PC.

What I want to accomplish:

I want a way to make the PC automatically power on when power comes up after power outage..either it can be BIOS setting or a software or a combination of softwares. If this is done, downloads n remote session can continue once pc boots up.

The things I tried to accomplish this but not successful are:

1. Browsing net & wandering over the computer shops to find a UPS with RS232 or serial port so that it can be connected to PC's serial port & configure power settings in windows xp such that UPS triggers PC to power on.
Result: There is no such UPS ( I am pretty sure earlier models of APC home UPS, around 9-10 years ago... had this feature).

2. Tried various softwares such as Auto power-on etc, etc
Result: These softwares can make the system power up automatically only from Hibernation state and not a fully powered down state.

3. Explored and collected Details on Wake-on-WAN feature for turning on the PC over WAN.
Result: somewhat confusing data. Also I have Dynamic IP so I cannot know what IP was assigned by ISP (once modem powers up after power outage) to be used for send Wake-on-WAN magic packets over net.
Tried tieing my dynamic ip with dyn dyns but not useful as PC needs to be up for dyndns to be updated with my new dynamic ip.

I request anyone who knows a way to accomplish this to let me know a way to wake my PC over WAN.

Some SUGGESTIONS:

I have noticed LAN port glows even when computer is shutdown, PC connected to power socket. Can there be a software made Such that PC can reboot at specific time if LAN port is active. I doubt Wake-on-LAN, Wake-on-WAN works based on this but not sure. any help would be useful!!