Hi Jenny ,
There are some uncertain things here , I believe you may duplicate it and export it . then you will have app with all reports or charts , Please try to open it once with desktop application. If everything is working fine then import it to server and published it and let me know if still your app doesn't open .
When you duplicate it to your work area does it open?
Before you delete anything you should have a backup or snapshot just in case. Or you could export the published app to your desktop so that you have a copy of it. If all fails then you could then just import this copy back.
Once I copy the app to my work area I in effect have a copy. So if I delete the one that is published I should have an exact copy of what I just deleted. If the duplicate is working then I would just delete the published one then publish the work copy.
Do you have any idea why it is not running? Was it working at some point and you made changes or added more data? I recently ran into a situation where with limited data my app worked fine. As soon as we loaded more data it did what you describe and never opened.