Hello!
I really don't understart what both of you mean by 'hold down the power button (...) gives me options to restart, sleep...'. I'm on a Macbook, late 2010 and such thing doesn't happen. Which Mac model are you using?
In any case, I found a solution to this problem and I haven't had any more trouble with the 'invisible' icons!
Here's what I did (suggested by an Apple Developer):
1. Open 'Terminal';
2. Copy this text (without comas): '' mv ~/L*/Application\ Support/Dock/*.db ~/Desktop ";
3. Press Enter; (Screen will flash and icons, dock & finder will disapear for some seconds! In the end, everything will appear on screen!
NOTE: On Lauchpad, some icons will have a new order! You can then put them in the order you whish to have them!
Apparently, this solves the problem and it doesn't happen again!
Hope I helped!
Best!.