MacBook Problem

When I turn on my MacBook, it brings up the password promt. I fill this out correctly and the screen goes blue and I can hear the fan turn on and everything begins to boot up...and then I am brought back to the password prompt. I assure you I am inputting the correct password. Please help. I miss my MacBook and until it is fixed I must use a computer from the stone-age (roughly). Thank you in advance for any advice!

Something's failing to load on startup. Try this: boot holding down the SHIFT key. Keep holding it until you see words "safe mode" in red. Then login using your normal password. If that works, then the problem is some login item is incompatible with your Mac. Visit Accounts, your account, and disable third-party login items, reboot normally. See if that works.