What happens when you enter snip in Start/Search and hit the Enter key?
If nothing then you may have inadvertently turned off the optional Tablet PC features, of which Snipping Tool is one (since 2005).
Click on Start button, and go to Control Panel.
Click on Programs link then Programs and Features.
Click on Turn Windows features on or off link. If User Account Control pops up for confirmation, click on Continue button.
Scroll down the list of features in Windows Features dialog window, tick the check box for Tablet-PC Optional Components to enable and show the Snipping Tool
Then it should show up under Start/All Programs/Accessories.