BIOS does not recognise the DVDCD drive 278

Have you tried swapping the cd-dvd and hdd on the motherboard connectors to see if the dvd-cd drive will work on the primary connector? (just to rule out the connector) You could also try the DVD drive in a different computer, again just to rule out the drive as the culprit (as well as other problems since the replacement CD drive had the same effect) It seems from your post that the HDD is working flawlessly so that is the reason for the swapping of primary and secondary recommendation

AS far as flashing the BIOS check your version (on the initial cold boot screen) and match that with what is listed at the Asus website to determine which flash is the correct one. Upgrading with an incorrect BIOS is not a good idea.(usually does not upgrade and will fail the flash). If you are "lucky" enough to get one that is incorrect and does flash you can get into some serious problems with the motherboard. If you saved the old BIOS it might be best to reflash back to the original version and make sure you are upgrading with the correct version. If you didn't save the old version then you may be looking at getting a new CMOS chip aka replace the motherboard, It's faster and cheaper then going through the trouble of replacing the chip.