Macbook doesn't start!

Hi, I'm trying to turn on my laptop but it doesn't start. The machine was off for several weeks because I've got a new one and after this was updated to snow leopard it doesn't used until yesterday when I turn on and after several minutes using it the keyboard doesn't respond and I proceeded to restart it and now on the screen only appears the apple logo and an charging bar that it start quickly and it disappears and appears again and after that the machine turn off. Please, if someone could help me. How could I fix this problem? or Which could be the the problem?

yes, it is fully charged and connected too. Even I was trying to boot from the snow leopard dvd without any response