I got this before while using Adobe Illustrator CS3.Here is how i fix it. Just ensure yr not in "Isolation Mode"while you see a "back"arrow by double check the top of your window, below the options bar.click that through until yr out of it.

you know, While yr in isolation mode, you wont be able to select or change other objects other than the objects in that area.

Here is a instruction to resize a selected object.

Firstly, select any of the white squares in the corner or along the sides of the bounding box.Notice the cursor changes to a double arrow.

Then click and drag the square to resize the object.

Thirdly, Hold down "shift"key whild yr dragging one of the corner squares.this way, you can resize an object and remain its proportions not being changed.

I know this is super later but I had this problem just now and searching the internet didn't help (maybe wrong keywords?)

Shift+crtl+B, it's called the bounding box, you've accidentally hidden it.