Keyboard issue

This is the second time this has happened: at some point during use of blender, the focus of my mouse and keyboard leaves blender and does not return unless I restart my computer. i.e. I hit tab to change blender modes, but instead a selection of my currently running programs pops up. I try to click on the blender interface ANYWHERE and I can no longer select meshes or alter data.

I have an ONN RF wireless keyboard and mouse. Running windows 7. Any idea what’s going on and/or how to resolve this without turning off my computer every time (takes forever). Thanks!