macbook white

Hey I'm new and I'm having a problem with my MACbook white. When I turn it on, the picture of the Apple appears and the loading circle thingy. But it won't load up my home screen. It stays in "loading mode". I hope I'm explaining this right. Basically the macbook won't load my screen where all my icons are. I can't get on line or even see my screen saver! I was told macs don't get viruses so what could be wrong? Please help!