I really think that your problem is PSU related.
All very well having the 4.8V but have u got all the correct voltages with reference to ground 0V ?
I forget the exact details but the motherboard has to have +12V, -12V, +5V , and -5V with reference to a good ground 0V
Hope that helps a little and that you haven't fried it - fairly unlikely and also pretty unlikely that you fried it with static during the install unless you were running around on a nylon carpet with trainers on at the time !!
Good luck