Updating my Mac n it won't turn on...?

Last night I had Checked for updates on my Mac then turned it off for the night...then this afternoon I turned it on fine but it said it still had updates it needed to perform so I did them then it asked if I wanted to restart it to finish the updates so I did...I waited a few mins and my computer never turned back on...so I pressed the start on n it popped up to the grayish page with the loading circle (not the wheel of death) and a loading bar under....oh! N the apple was of course on the page too...but the bar would start to fill in then disappear, then reappear n start to load, then disappear again and after it did that a few times it shut off again...:/ what do I do? I tried all the unplugging stuff n pressing the keys like it says in the manual...am I supposed to just let it sit for a while? Please help me!