There was a problem with using Presentation in Google Docs this morning. As you can see in the Google Apps Status Dashboard, this was addressed quickly by Google and was completely fixed less than 2 hours later.
To help you find out this information on your own, a link called "Is Google Apps broken?" was added to the links for Google Apps. If you ever experience problems with Docs, Email, etc. you can click on that link and find out if its a problem that Google is already working on.