Did this happen all of a sudden?
Have you ever been able to see Code view?
Please share more details like
1. Which version of DW are you using?
2. Which OS you are in?
3. Code view blank is seen with some particular file or with all files?
However we are aware of one of the issue where code view doesn't load in DW CC 2017 and later releases. Which is being prioritized for fixing.