you have "sticky keys" enabled. If you press the shift button 5 times in a row, you enable it (Win XP -- not sure if it's in earlier versions). This function is for the disabled and allows the user to push a series of buttons one after another (say ctrl alt delete or ctrl S) and it will react as if you have pushed all these buttons at the same time.

Sometimes if you also push Control and either Function or Shift together for a long period too, it does weird things like select a whole paragraph for you or bring up alternate menus on you. It happens to me all the time in Photoshop. I get different cursors, etc. I forget what it's called. Anyway, to fix it, press control and alt together for a long time say 5-10 secs and I find that it goes back to normal.

Sometimes restarting the computer also gets rid of it too. A little drastic but I had to do it, coz I couldn't figure out what I had done. *G*

:-D