Start menu pops up unexpectedly

I have a friend running Windows 7 Pro on a Dell Latitude XT2 tablet. At apparently random times, but especially when she launches Excel (2007) the Start menu pops up. If she happens to keep typing while the menu is opening, it begins a "search" for an item that matches the last key she typed.

I asked her if Excel was trying to set itself up again, but she said not. I told her to look for a stuck key and to try holding down the Ctrl key and hitting the Esc key a few times but these had no effect. Any ideas?

Thanks for the unbelievably fast reply Richard. We will try it and post the results.

I finally got my hands on her tablet to check it out. The search angle did not yield results though. Here is what I tried:
(1) back up registry,
(2) modify the HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Explorer\DisableSearchBoxSuggestions key to value 1 (actually I had to create the key),
(3) close registry editor and re-boot.
Still had popups occurring.

While playing with the tablet, I noticed that the popups only occurred when Excel had one of a small group of spreadsheets open. So I tried saving one of the .xls files as .xlsx, but this didn't help. Tried running Office Diagnostics, again no help. Searched the offending spreadsheets for macros, but they contained none.

Stepping back for another look at the problem, I noticed that the cursor always jumped to the lower-left corner of the screen when the popup occurred. This suggsted that the tablet inputs might be causing the problem. I ran services.msc and stopped the Tablet PC Input Service ... voila, no more popups!

So I ended up writing two small scripts, one to stop the tablet input service (sc stop TabletInputService) and one to re-start it (sc start TabletInputService) and made run as administrator shortcuts to them on her desktop. So while the problem is not solved, she at least has a workaround which will allow her to use Excel productively providing she stops the service before using Excel and restarts it when she is done with Excel.

reinstall windows if all else fails. :)