This is an instructable detailing how to create a keyboard shortcut so that you can quickly switch to screensaver at any time.
Step 1: Creating the Shortcut on the Desktop
Go to the folder C:\Windows\System32 and sort by filetype. Look for the screensaver file type (.scr). Find the file scrnsave.scr (you can choose any of the screensavers, this is the black screen one).
Right click and select send to>desktop (create shortcut).