cutting through all the technobabble, it's been my experience over fifteen years of repairing and refurbishing PCs, that when a computer says "no boot device found" that 95 times out of a hundred, it's because the hard drive has failed.
you can try the freezer trick... place the hard drive inside a zipper bag, freeze it for twenty-four hours, and then try to fire it up. This can sometimes give you a few minutes to an hour to recover any files, but it is a temporary fix at best. if you NEED data off of the drive, there are services such as Ontrack that you can mail the hard drive to who will try to recover the data, but these services typically start at $250 and go up from there. (quickly)
less likely culprits of the "no boot device found" error are that the power supply is failing and no longer pumping out the voltage needed to spin the disk, or that the SATA channels on the main board or CPU chip have gone bad. Both of these can be ruled out by plugging the drive into a different machine or an external housing and seeing if it will operate. Cables are almost never the cause unless you've been mucking about inside the case beforehand, in which case it probably came unplugged or got pinched. And this is all but unheard of in SATA cables, which are very robust by design.
