Google Drive is currently experiencing an API outage that means that you cannot load existing, or create new diagrams using Google Drive on draw.io. Google will post status at https://www.google.com/appsstatus#hl=en&v=issue&sid=4&iid=c708d68b1884a629816e361895c125a5.
The only possible workaround, currently, is if you have your draw.io diagram(s) synchronized locally, you can drag and drop those files into https://www.draw.io/?mode=device and access/edit them. If you edit them you must remember to save it to your local device and replace the file in Google Drive, afterwards.
We will post any updates we hear.
draw.io is a free to use online diagramming application, with some pay-for exceptions for particular integrations. You can store your diagrams in Google Drive, Dropbox or locally on your device filesystem.