how can i lock desktop icons in windows 8

Your display drivers are different.

Guilhad, you have a generic Intel video display driver as seen in the header of you version of the dialog box.

Greg has a High density Flexview Display driver - see his dialog box header.

Greg's video display driver supports display resolutions higher than his monitor can display all at once. Yours does not. His screen becomes a movable window on a screen image that is larger than his monitor, when using HIGH resolutions. You move that window around on the display image by bumping the mouse pointer against the screen edges. This is the autoscroll you see in his dialog box. When unchecked, you are required to do something like right click and use scrolling controls there or use arrow keys to scroll the screen. He alluded to this when he mentioned "more icons than will fit on your screen". 

This has little to do with the Windows 8 / 8.1 issue of unstable Icon positions, though it may interact with the issue on his machine. He may see different effects because of this specific display diver.

This answer does NOT work.

My "auto arrange" is not checked and my icons re-arrange anyway.

This thread started on icons moving around on the screen, being displaced, moved to a second monitor, etc. You can see this in the first few posts.

It really is not about auto arrange, a different situation. Why not move that question to a different, and more appropriate thread, since the original problem is still NOT solved for all users experiencing this.

Back to the topic: since apparently my problem was solved since I have a particular high resolution driver, is there a registry entry that controls the "autoscroll" function?

Maybe that is the solution for the other people who still have the issue.

Regards, Greg

Greg is right. One topic at a time is best. Usually. . . 

1. Icons reverting to a previous arrangement while only using one monitor.
2. Icons jumping to a different monitor.
3. Icons re-arranging when disconnecting another monitor.
4. Icons scrolling off of the viewable screen.

These are all mostly separate issues with desperate causes. They are all probably related.

Thoughts:

Windows Desktop is, at its root, is a folder like "Documents" or "Music".  It has some unique properties that make it display as the desktop we all depend on.  Having the ability to re-arrange in the folder columns as we see fit, and automaticly rearrange on the desktop to fit all in a smaller resolution when we need it has got to be complex, and aparently has conflicting functionality that manifests across multiple Windows platforms, complicated by Manny different video drivers with different functionality.

My solution to scenario #1 above was to use an app that records your Desktop arrangement and allows you to restore it with a right click menu option on the desktop.

"Desktop Restore" by Jamie O'Connel.

I even have icons disappearing after I reboot.

This is clearly another error in Windows 8.1

It is clearly way past time that Microsoft fixed this annoying problem.

What kind of company would not deal with this issue for so long?

Richard