OS driver issues seem a tad unlikely if it is not even seen in the BIOS. First thing to try is to go into the BIOS and choose to restore default settings (it is called slightly different things in different BIOSes). Next thing to try is to open up the box (remember to use anti-stat gear!) and disconnect / reconnect the power cable to the drive, and the same with the data cable at both ends - it might have come loose. If it is IDE and there is another device on the same channel, disconnect it and connect the DVD instead - if it works at this point, you might have a bad cable or the other device might be faulty and could be messing up the IDE bus. If this doesn’t help either, clear the CMOS memory - the motherboard manual should explain how to do this.
If you still can’t see it in BIOS, you probably have a HW fault. Things to check:
*Try replacing the cable - if you have a spare one, use it, otherwise, borrow the one used for the hard disk(s) (assuming both are SATA or both are IDE).
*Try moving it to a different SATA/IDE connector on the motherboard (depending on what you have). If this helps, your motherboard had probably gone a bit gaga in old age.
*Test the DVD drive in another computer
*If none of that helps, I expect your motherboard or PSU has gone daft - while system hanging can also often be caused by bad memory or poor cooling, that would not explain the DVD drive becoming invisible. In many BIOSes, you can check what the different voltages are that are delivered from the PSU, these should be within a few percents of nominal.