Here's a quick tip for a Saturday morning.
When this happens, you need some way to close the offending web part. To do this, go to the Edit Properties page for the page that contains the bad web part. If you scroll to the bottom of Edit Properties page, you will see a link to Open WebPart Page in maintenance view. Click on this link.
From the Web Part Page Maintenance page, you can select the web part you messed up and then either Close it, Reset it, or Delete it.
Ah! You're back in business!