why my imac does this and helping to resolve the situation

[sami-jami]

Hey,
few days ago, i just turnt on my 24" imac and started with the white screen with the apple in the middle [like normal] then a grey tint ran down the screen saying i need to restart it, so i did, and it did it again. so i restarted it. Any ideas whats going on with it? and i think i have Leopard 10.5.8? so can i just update to Snow Leopard from that? or do i need a new hard drive or something? x

 

[Intell]

Could you start it up and right after the chime press and hold the Command and V keys. This will cause the computer to display a lot of white scrolling text. Could you tell us the last few line right before it stops?