If you ever use the Windows Snipping Tool and you have Trusteer Rapport installed, you may find that the Snipping Tool makes your screen go grey instead of behaving normally.
I found a video explaining that this is a feature of Rapport to prevent screen captures of your online banking site, which makes sense. What wasn’t clear, though, is that Rapport will do this if you have any open tabs that are on protected sites, even if you’re not looking at one of those tabs at the moment.
To make the Snipping Tool behave normally, find the tab(s) that are on sites protected by Rapport and close them. Voila!
(If none of the above makes sense, feel free to ignore and/or be impressed by the techno-babble.)