ITT: Post your bizarre crashes/bugs

Everyone has had this happen at some point - happily working on your computer, only for something to go wrong for no reason. So why don't we all post our most recent crashes or bugs that defy explanation?

My most recent one was that as usual the wireless network was losing connection. Nothing unusual, it goes back to normal if you turn off the router for an hour. However, when we turned it back on, i still couldn't get anything, but my dad could. So since Saturday i had no internet, and just found out why - somehow the damn computer had lost its static ip address. It couldn't connect to the network as a result. I don't know how this happened but it was a true pain. Anyway, knowing what was wrong made it easy to fix, and as you can see i'm back online.