slow boot up vista

running amd athlon 64x2 daul core 4 gb memory 300 gb h/d. My problem is on boot up, the first screen shows all the computers set up data then onto blank screen with a light blinking in top left corner, then screen goes blank for appox 45-50 seconds before bring up the microsoft bar with the green fashing bar to show its loading, then blank screen again , then the mouse pointer shows up on the blank screen and then eventually the vista logo , then it starts to load my programs . In all about one & half minutes to two mimutes, my system is free of any viruis etc/.
kind regrads ken.