How to show the disappeared DVD drive letter in Windows 7

Your DVD drive may disappeared in Windows 7 even BIOS has detected it.
These are the steps to resolve the problem:

1. Click Start, click Run, type REGEDIT, browse to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E965-E325-11CE-BFC1-08002BE10318}, then delete both UpperFilters and LowerFilters in the right-hand pane (UpperFilters.bak and LowerFilters.bak entries can be ignored). 

2. Hasn't seen yet?  Click Start, type Disk Management and choose the "Create and format hard disk partitions" link. If your optical drive is visible here then right-click it, select Change Drive Letter and Paths, click Change and choose a new letter. If the drive is now visible in Explorer, then repeat the process to change the drive letter back; if it's still not visible, reboot and it should appear.