Can't Recognize>> NEW <<
Confuse your victim by changing all the icons on the computer desktop. Just rename all the icons to whatever you want. Then change the icon pictures: right click on each icon, choose "Properties" then the Shortcut tab, then "change icon."
Submitted by agmisabeast
Incorrect
If the victim uses Microsoft Word, go into the victim's computer and change the auto-correct feature so it misspells common words. Just open Word, choose "AutoCorrect Options" from the Tools menu, and have it replace common words like "the" and "and" with wacky words like "eggplant" or "Uranus." Be creative.
Dark Side
On most computer monitors, if you turn the brightness control all the way up and the contrast all the way down, the screen will appear to be blank. Do this to your victim and they will drive themselves crazy trying to "fix" their "broken" monitor.
Spell It Out>> NEW <<
Rearrange the letters on your victim's keyboard to spell "APRIL FOOLS". You'll need to borrow an "O" and an "L" from a similar keyboard so you have enough letters to accomplish this.
Lost Buttons
Go to Start->Settings->Control Panel and find the option for your Mouse. On the Buttons tab, change the buttons configuration to switch the primary and secondary buttons of the mouse. Now when the victim clicks with the mouse, nothing will work as expected.
Cursed Cursors
This idea is great for playing a prank on your co-worker in an adjoining cubicle. Plug an extra mouse into one of your victim's spare USB ports and snake the wire back into your cubicle. When the victim is working away, give the spare mouse an occasional small nudge. (This is especially funny if your victim is actually trying to use the mouse at the time.)
Submitted by Dodger
Search Confusion>> NEW <<
Change the settings on your victim's computer so when they Google something their search page is in a different language. Just sneak onto their computer, go to Google.com, choose "Settings" in the upper right, then "Search settings." Now change the Interface language to whatever language you prefer. You can even choose Klingon, Pirate, Elmer Fudd, Hacker or Bork, bork, bork! (To fix after the prank just click on the "Google.com in English" link below the search box on the main Google page.)
Submitted by Stantheman
Away From Home
Change the victim's homepage to something unexpected. Open their browser and choose Tools->Options and enter the URL for a new page.