I must have accidentally clicked something in Photoshop because all of a sudden my rectangular marquee tool is not working correctly.
When I use the rectangular marquee tool to, for instance, surround something I want to delete on a document, it immediately does one of 2 things:
It turns into a rectangle with rounded edges, or
A box pops up on my screen that says
WARNING: No pixels are more than 50% selected. The selection edges will not be visible.
There is an "OK" button in the lower right hand corner of that box. When I click "OK" the box disappears but so does my rectangle on my document.