If that is your only computer, then you'll need the help of someone with a disc containing formatting software. I'm not sure why your computer does not recognise your dvd reader. This cannot be a new problem or you would not have been able to try out Windows 8, it sounds like a BIOS problem to me, That is of course if all cables are connected.
If you have another machine then perhaps the easiest way is to download a Linux 'Live' cd/dvd and use the formatting software on that. Of course if your 'duff' machine still does not recognise the DVD reader then you are up the creek I'm afraid. There are ways of resetting the BIOS to factory state, but they tend to be motherboard specific, again looking around the web with details of your motherboard should find the answer to that one.
Best of luck,
xy
Lons gives another answer which should help.