Many of the users of Windows 8 Beta that is the Consumer Preview are reporting that their DVD drive is not being shown. I too had this problem. I could install Windows 8 CP, could boot from DVD but after install of Windows 8 CP, the drive is not shown when a disc is put.
Some of them also reported that if you boot with Windows 8 bootable DVD in drive and ignore the boot from DVD message, then the DVD drive is shown, but for other discs its not. Anyway a Solution , A registry patch has been provided by Microsoft Employee Atishay. And it solves the problem.
1. Run Command prompt in Admin mode. For this type cmd in metro UI & press ctrl+shift+enter to get the cmd Window.
OR in Desktop , just move the cursor to bottom left and right click to get access to various Systemmanagement tools and from their choose Command Prompt (Admin)
2. In the Command Prompt Window just type & enter
reg.exe add "HKLMSystemCurrentControlSetServicesatapiController0" /f /v EnumDevice1 /t REG_DWORD /d 0x00000001
And reboot. Now insert a disc to test.The drive will be shown.