If anything flashes threw the digital pins on start up it will be so quick it won't effect anything.
Your sentence there is a bit broken. I assume your wanting to use the arduino to power on or reset a PC? To do this you don't want the power and reset to be directly wired to the Arduino. I suggest you have the PC connect to a pair of relays and have the Arduino actuate the relays. One that actuates on 5V. The you can digitalWrite HIGH to a pin that connects to the relay. The Relay will then actuate and turn on the PC. Here is a slightly modified version of the button example.
// constants won't change. They're used here to
// set pin numbers:
const int buttonPin = 2; // the number of the pushbutton pin
const int ledPin = 12; // the number of the relay pin
// variables will change:
int buttonState = 0; // variable for reading the pushbutton status
void setup() {
// initialize the relay pin as an output:
pinMode(ledPin, OUTPUT);
// initialize the pushbutton pin as an input:
pinMode(buttonPin, INPUT);
}
void loop(){
// read the state of the pushbutton value:
buttonState = digitalRead(buttonPin);
// check if the pushbutton is pressed.
// if it is, the buttonState is HIGH:
if (buttonState == HIGH) {
// power on to relay:
digitalWrite(ledPin, HIGH);
delay(500); // allows power to the relay to stay on long enough
// for the PC to power on. this number may need to
// be adjusted
}
else {
// send no power to the relay
digitalWrite(ledPin, LOW);
}
}
Of course the button will be replaced with whatever means you plan to use to tell the board to actuate the relay.