Re: A bootable device has not been detected
Bring your specs to the table but there are only a few real possibilities here...
1) Your hard drive controller has failed.
2) Your hard drive's Master Boot Record has failed or been compromised.
3) Your hard drive has physically been damaged.
4) Your power supply is no longer supplying the proper voltage to the drive.
5) Your BIOS has failed or been corrupted.
(4) is generally easy to check, see if your hard drive tries its initial spin up when you turn it on. Also, really unlikely since your computer at least starts to boot up; usually power supplies just quit altogether. If it makes a sounds like it spinning, it probably is, but make sure you don't mistake it for fan noise.
(1) is not all that common; and I don't think your symptoms warrant checking it out, yet.
IF its (2) or (3) (i'm not saying it is) you're going to need a new hard drive, and someone else can explain all the challenges you'll face if that comes up.
And if its (5), you're looking at probably getting new motherboard, or (on some boards) a new bios chip.
Remember, I didn't say what it was, and you should still come back with your specs.