Help screens have disappeared

We're working in WP 3.2.1 MultiSite with BP 1.2.10, and we're gearing up to open on Tuesday. We were working away, and all of a sudden I notice that all the drop-down Help screens in the Dashboards - not just on our main site, but in all our test user blogs, too - have disappeared. The Help tab is still there, but there's nothing in the un-expanded box. I checked, and there's nothing in the page source, either. (However, the Screen Options tabs still work correctly.)

I've tried backtracking by removing the last plugins we loaded; but nothing has worked. Note that I have around 60 plugins loaded on this puppy; so it's not practical at this point for me to try removing every one - especially when everything else seems to be working fine.

Anyone know what would cause this? Any illumination would be much appreciated - especially seeing that we customized all these dashboard Help screens, and they could be very handy to our upcoming users. My thanks in advance for anything you may know --