Flashing Blue and Yellow Shield on Windows Taskbar

Can't go to other programs, can't do anything..

What to do?

CTRL-ALT-DEL gives you a menu, now pick Start Task Manager.
Once TM starts, you'll see, under applications, which one this is - select that and then click on Switch To.

Now you can interact with it.

http://www.askmefast.com/What_does_a_flashing__blue_and_yellow_shield_mean_on_my_lower_taskbar_which_stops_me_going_any_further_with_using_my_computer-qna1580513.html