how to start the system automatically

Check if your BIOS has options to switch ON with alarm
Also you can try modem triggered switch ON if u have always on connection !!

Could u be more specific with your question??

i want the system to turn off when the power goes out and start again when the power comes back again without any ones interruption

You need a UPS for that...

If you have a UPS, and if it has a computer interface, you can control it from your comp. Then you could do what you asked.

Turn on Restore On AC Power Loss in your BIOS

This item specifies whether your system will reboot after a power failure or interrupt
occurs. Settings are:
[Off] Always leaves the computer in the power of f state.
[On] Always leaves the computer in the power on state.
[Last State] Restores the system to the status before power failure
or interrupt occurred.

either use a UPS, or make a circut for it yourself. But remember - the max it can do is to turn off power. Logging off or in needs drivers.

For shutting down on power failure u definitely need UPS.
As far as restarting when power comes back, it depends on your BIOS check if it has option to Switch on on power resume.

Do u have UPS, if positive u can configure it from Power Options in Control Panel to suite your needs !!

i do have an ups when i try configuring it asks me to select a com port but my ups isnt connected to one must my ups be connected to a port?

Obviously... do you expect your UPS to communicate with your computer via your power cord?