Unable to boot up imac

[Aristor]

I was awoken last night at 3 in the morning by the "ding" the imac makes when booting up. I had left it in sleep mode in my windows partition of boot camp. I tried to log in to turn it to sleep mode so I myself could get back to sleep (mode) but I was unable to log in. The imac was stuck on the apple logo, with a spinning circle below it. Exhausted, I used a hard shutdown to turn the computer off. I woke up this morning trying to log in, but it blocked me from booting up.(into either OSX or Windows) I have a late 2011 imac, I use OSX lion, I have no usb peripherals, I have tried restarting holding down option, command, command-option-P-R, & shift. I am not sure what to do now, and I need this computer now. Thanks in advance for any help you can give.

 

[xkmxkmxlmx]

What do you mean by "blocked you"? What do you see? Does it power up at all?