If lately you have been experiencing a short delay when trying to take screenshots by pressing the Print Screen button (PrtScn), it’s most likely because of a delay setting in the screenshot accessory.
Go to Application → Accessories→ Take Screenshot. You should get this window:
Change the delay setting to 0. You should have to take a dummy screenshot for the change to take effect. After you do that, when you press the PrintScreen button you will be getting screenshots without the delay.