Lets check this out.
1. Press Print Screen. Open Wordpad. Click Edit - Paste. See if you are able
to paste the contents in Wordpad.
2. If yes, that means you are still missing something in Paint Brush and
i.e. wrong selection of a tool.
3. If no, then click Start - Run - type:
%windir%\system32\clipbrd.exe
Check if your Print Screen contents are there in ClipBoard or not.
4. If the Print Screen Contents are not even available in ClipBoard then try
press ALT+PRINTSCREEN and check both the above options again.
5. If that also not working then try just copying simple text from one
document to another. See if you are able to do so and this will clear that
the problem is only with Print Screen function.
6. Moreover, if you are trying to PrintScreen a web-site then could be
possible that they have blocked this. I don't really know that it could be
possible or not but you can read the article below if that is your problem:
http://blog.gilluminate.com/?b=20060425123338
Hope any of above helps you, let us know!