How to power up a Compaq persario externaly Including wiring an external power button?

I have a Compaq persario v2000 i want to make it a car computer im all but finished the last thing holding me up is how to turn it on externaly. I was wounderin if i took out the battery if there was some way to turn it on every time it recived power ie key turned on. Or how to wire an external power button to it any help would much be appriciated.

You might be able to accomplish this one of three ways. The easiest one, rigging an external switch, would be as simple as wiring a momentary switch parallel to the power button inside the tower. However, the driver would have to manually switch it on and off. For what you want, it requires a bit more work. If you look at the ATX power cable running to the motherboard, there will be one green wire. This is the power on pin, and when held low will switch the computer on. I would wire the +12V switched power from the ignition to a relay that shorts this pin with ground. When the car is switched off, however, the computer will lose power immediately - thereby preventing a proper shut-down. Using this method, I'm not sure how to automate a shut-down. The third method might be to use the brains from a UPS (you would need one with a USB or a network connection to the computer). Rig it to detect the switched +12V from the ignition (but don't use this as the primary power - not enough current and you'll blow a fuse). In software on the computer, instruct the computer to shut-down the instant power is off. This is obviously the most difficult way, and one where I'm unable to furnish any more specific information. Good luck. Let me know how it turns out.