Nebastion, few questions:
1. what version OS are you using?
2. which macbook model?
3. what occurred before/during you last shut it down?
4. did you do any updates recently?
5. have you looked at this:
http://support.apple.com/kb/TS1367
6. did you try this too:
PMU Reset
a. turn the computer off.
b. unplug the power cord & the battery.
c. hold the power button down for 5 seconds.
d. replace all the power components, and then start up again.