Try one of these...
Found several solutions on W3, but the best is No1 in the list. No2 worth a check, though.
1. I had this problem w/Windows 7-32Bit and found that if I right-clicked on desktop and then clicked "Refresh" the icons stayed in place after a reboot. You'll have to do that anytime you add/move icons to keep them 'locked' in place.
2. The problem was that one of the monitors was not being detected by Windows correctly and therefore reverting my display profile to a default configuration. Once I remedied the problem of Windows identifying my monitors the problem went away. It turns out that one of my monitors was set to a refresh rate of 59Hz instead of 60Hz. Once I made the change to 60Hz I retained all changes made to display properties and icon positions on a reboot. I would suggest that you look into the settings for your monitor(s) and verify that they are correct.
3. I have the same problem, I reboot window 7, all my icons are arrange to left side of the screen. I found, my problem, was I didn't install the video driver (Nivdia driver), I was using the default microsoft driver. that will keep arrange the icon to left, every time. Once, I got the video driver install, everything work just fine.
4. I unchecked all of the non-Microsoft services in msconfig and restarted. All the icons stayed put.