screencapping question

OK, so I'm attempting to make a screencap from a DVD. Using PowerDVD, I paused the episode where I want the cap, pressed the printscreen key, and pasted it into PSP. But, I only want a piece of the cap and every time I try to crop it, it doesn't crop in the spot that I tell it to.

Oh, and here's another problem I just encountered. When I saved the cap I took to show you guys, it apparently saved with a black screen.







Help!!