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
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.