Although it may seem that nothing is going on, you are actually slowly but surely uploading your file to the Discussion Forum. If your file is very large, it can take upwards of an hour to upload. Small files work best as Discussion Forum attachments. If you need to attach a really big file to a Discussion Forum post, think about emailing your course TA the file (or sharing the file via OneDrive with your TA) instead. Contact your course TA first to make sure that this is OK with them. Some assignments require that you post your final document to the Discussion Forum for everyone to see. In that case, you'll simply have to be patient while the file uploads.