We've made some changes to how missing files are handled with the recent 8.0.4 release. If a file has gone missing, it will prompt you to find it upon opening the project. If the file has moved, you can point to the new location and the project should open normally. If the file has been deleted, answer 'no' to finding the file, the project should open, and any instances of the file on your timeline will show as 'offline' media. Offline media will have no effect on your produced output. You can either leave those clips as-is, remove them from your timeline, or it may be possible to update them to point to a different file under certain circumstances (swapping out an image or audio file are two common cases).