ALT-PrtScreen will capture the Active Screen to clipboard. 
PrtScreen alone will capture the entire screen vs. the Active.

Then need to open image editor like Paint.  (Start/Accessories/Paint)

Edit, Paste from clipboard, modify,crop, rotate, etc.

File, SaveAs filename.bmp

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The screen capture works on many keyboards but your may differ.  If in DOS mode, using PrtScreen will send to Printer vs. capture to clipboard.

Also many utilities available for screen captures.  I use freeware HardCopy but there are many others out there.