Hello Evandro,
Thanks for posting your question to the forum. Can you try deleting the file and uploading it again and see if the same thing happens. Note that depending on how complex the DWG is, it can take a little time for it to do what we call translate so that it can be viewed in your browser.
If that still fails, can you try creating a DWF or DWFx of the file and upload that to see if it's viewable.
Also please let us know how this goes and Happy Holidays.