AutoCad 2D :: Selection Interface Not Working?

I am working in AutoCAD 2011 and, all of a sudden, both left- and right-click stopped working properly.

Right clicking only repeats the last command, either with or without any object selected, even though my personal customized preference has been set to Edit when an object is selected.

But most worrisome is the left-clicking situation. Double left-clicking does nothing, instead of the usual editing it had been doing all these years.

When I single-left-click an object, it seems to select it (grips appear and the object lines appear dashed, just as usual), but if I want to do something afterwards, it does nothing. For example, I select (single-left-click) an object and press the delete button, and it does nothing. Also, despite the object being selected (in appearance at least), I noticed that the "Layer" and "Properties" toolbars don't change, thus, not displaying the correct layer and other properties of the said object.

The way around this seems to be to type the command first and then select objects (which means that the commands work properly). But after more than ten years working the other way, you can imagine this slows me the hell down, almost to a point of continuous stand-still.

Also, we opened other programs to see if the mouse and keyboard were simlutaneously broken down. Of course theye weren't and, in the other programs, left- and right-click and "delete" funcitons were working properly.