I am looking for a transparent screensaver. Or a way for there to be no screen saver, but instead of locking, it disables the mouse and most of the keyboard, until I hit an unlock key.
Yes that is possible - I do not remember now exactly which screen saver it was.. but it was long time ago on XP
But here are some other pranks that could be .. funny..
A classic computer prank never goes out of style. The desktop image trick has been around for a bit, but rest assured: There are plenty of unsuspecting victims still to be found. Just head over to an unattended computer, minimize all the windows, and hit the Print Screen key. Paste the captured image into any graphic editing program — even Microsoft Paint will do — then save the file and set it as the desktop background. Then, all you have to do is hide the actual icons on the desktop — put them in a folder somewhere — and your victim will try endlessly to click the nonexistent icons, which are actually just part of the background image. For another variation, leave one program open when you capture the screen and watch as the person tries to click on it, type in it, and close it to no avail.
There are few things funnier than forcing a friend to insult himself — and Microsoft has made it easy to do just that. Take a moment to edit the Autocorrect feature in your colleague’s Word or Outlook (it’s in the Tools menu in both programs). Add a new entry to replace their name with “douche,” and watch how much more interesting all their emails and documents will suddenly become. A little creativity can take this one in plenty of different and equally entertaining directions.
The Wrath of Rotation
A simple but quick and always amusing prank is putting the screen rotation hotkeys to uses Microsoft never intended. Just run by a co-worker’s desk, reach over and hit Ctrl-Alt-up or down to rotate their monitor orientation. If you have some alone time, you can one-up it by also going into the Control Panel and setting their mouse to left-handed. They’ll spend 10 minutes with their head tilted sideways trying to figure out what the hell is going on.
The laser mouse may have ended the era of mouse-ball stealing, but it opened up another option. Stick a few layered pieces of transparent tape on the bottom side of your friend’s mouse to really mess with its functionability. Or, for bonus points, tape a small Post-It note that says “Why won’t my mouse work?” over the laser.
Back to the computer for some more advanced antics. This one may be more suited for a close friend or significant other, as you’ll have to install something, and you could probably get fired for doing it at work. Set up a VNC (virtual network computing) server on their system. You can find free ones like TightVNC for Windows or OSXvnc for Macs. Once you get through the configuration, you can click, type, and do anything on their system from your own computer. Do some subtle things like occasional keypresses or program launches and see how perplexed they become. We don’t recommend keeping this up for long, though, or you may suffer serious consequences with their anger (and you may also witness some disturbing pornographic habits as an unintended side effect).
Use ClearLock, you can set an password and it covers the screen in an translucent screen and you can unlock it only using an password.
Have a look at Transparent Screen Lock PRO. It is pretty much exactly what you are looking for. There are added benefits, not only can you unlock using your Windows username and password, you can assign other users, or groups of users to be allowed to unlock using their username and passwords. These unlocking actions can be logged so you know who unlocked your system.