Install Asus PC Probe from http://download.asus.com.tw/mb_dl_menu.asp?l1=1&l2=15&l3=8&mid=3 if you can. Tell us the numbers it gives you for CPU temp, MB temp, CPU fan, +5V, +3.3V, Vcore. Knowing those numbers would rule out your power supply and cooling as causes of the crashing.