Hi Kristy,
I'd look at a couple of things. First, have you verified your site in Google Webmaster Tools? If not, do so now. If you have, log into your account and see if you have any messages saying an action was taken with regards to your site.
Second, you haven't made major changes, but even a minor change in the right part of the code could have caused your analytics to stop working.
Before we get into full-fledged panic mode, let's do a little diagnosis. Take a deep breath, and go back to your analytics and get a little more information.
- Is it just that one page that suddenly has no entrances?
- Is your site traffic as a whole down?
- For that one page, what was the source of those entrances? Was it a link on another site, and that link has been removed?
- If the source was organic search, has you traffic declined over all search engines, or just one search engine?
If we figure out more exactly what the problem is, we can help you get things fixed back up.