I installed the Analysis ToolPak add-in this morning, was using it for a
couple hours, and now it's disappeared. No idea why- I haven't mucked with
any of the Excel settings in the meantime. I've tried restarting and no
luck. This is really frustrating- it shows up in the list of Add-ins, but
when looking at the set of commands I can add to the ribbons etc. Data
Analysis has completely disappeared.

Thanks in advance for your help.