My graph suddenly disappeared from my web monitor display. What should I do?

Clear the Web browser cache.

Note:
Note that when the cache is cleared, it may take a few seconds to load pages when you visit them for the first time, but on and after the second time they will be displayed as quickly as before. When you clear the web browser cache, all previously displayed temp files and cookies will be deleted.

Deleting the cache in Internet Explorer
On the Tools menu, click Internet Options > Temporary Files > Delete, select the "Delete all offline contents" check box, and then click OK.

If using the Java Runtime (Sun Microsystems), perform the following procedure.

Java Runtime 1.4
In Control Panel, click Java Plug-in to open the Java Plug-in control panel. Click the Clear button on the Cache tab, and then click Yes in the confirmation dialog box.

Java Runtime 1.5
In Control Panel, click Java to open the Java control panel.
On the Basic tab, click the Delete Files button under Temporary Internet files, then click Finish in the confirmation dialog box.