Different software packages may handle the keyboard shortcuts differently. Are you doing this between two notepads or within a Word document?
Are the keys physically working?
Possibly something you have running may be effecting this. There are net topics about this, so I will do some research. It seems I remember someone had a registry patch, but I do not remember what it was.
You can try some of these, not in any specific order:
1. Have you tried a different keyboard? The CTRL\SHFT key may be stuck or damaged\shorted from spilled coffee.
2. Try reinstalling the keyboard drivers. (Also, try to SHFT-v\SHFT-c in safe mode. If it works there - it's definitely a problem with the driver.
3. Try to copy\paste with a different shortcut... CRTL-insert to copy and SHFT-insert to paste. If they work, it's a problem with your keyboard.