So this means the Mac cannot find a bootable device on your machine. If you hold the option key after the chime do you get a list of devices to choose from? At minimum you should see your hard drive (usually labeled Macintosh HD). If you don't see anything then you need to figure out if the drive has failed or the drive cable. Easiest way to do this is to remove the drive and put it into an external USB enclosure and attach it. Then do the option thing after chime and you should see the drive attached and can select to boot from it. If it boots normally then likely your hard drive cable has failed (very common issue and cheap to replace). If it still doesn't see it then you might be looking at a bad drive that needs to be replaced.