Sorry to hear about the trouble. Please ensure that you have the latest version of XD which is 37.1. In case if you do have the latest version, please try the steps shared below:
Sign out of XD and CC Desktop app.
Close CoreSync and all the Adobe-related processes from the Task Manager/Activity Monitor.
Sign back on the CC Desktop app and launch XD from there.
Check if you are able to access the cloud documents?
If you are still unable to access the cloud documents, please check if you are able to see the documents here: https://assets.adobe.com/cloud-documents and also share a screenshot of the About XD info page.
If no, please ensure that you are signed in with the correct Adobe ID using which the documents were initially saved. If you do see the documents there, please share a screenshot of the About XD info page.