Hi there, @sparramore09, thanks for reaching out to us.
Just to clarify, because your title says 'online', but in your message you mention the Dropbox folder, is this issue on the Dropbox website?
If it's on the website, when you preview the file, do you see the 'Open in' option to open the file with 'Excel for the web'?
How about if you try from a different browser or from a private browsing window?
Keep me posted.