Hi Kat,
Check your user prefs.
You probably have the “Pie Menu on drag” enabled. This means you need to hold Tab and drag the mouse to bring it up.
I wouldn’t suggest this is a good option for most people’s workflows, but if you do anything other than just modelling meshes in Blender, I would suggest swapping the Tab and CTRL Tab functions.
(ie the “Tab for Pie Menu” option below)
