Hey check the bios on your computer and see if they are on or off...if they are not there........Then go find your bios on the internet dowload the bios if they are not there just go to what ever kind of computer you have website and look for there to download the bios at the website..... hopefully that helped a little bit.
Ok so umm restart your computer and when the first thing comes like when it says the computer name press F2 or something like that and go in to that menu and look in the bios an see if they are on or off.... if that hasn't helped you PM a/k .
even if its not on the bios, it should still open up when your press the eject button. my best guess is that the power cord that comes from the power supply got disconnected. if you know how, you might want to open up your computer, and see if it is disconnected, and if it is, put it back.