[ergo]

My desktop picture/entire screen have been covered with a white screen/background; when I first start my machine up my desktop picture appears for several seconds and then is overlaid with the white background.
When I shut down, my desktop picture appears for a few seconds before quitting.
What could have caused this anomaly and how can I fix it?
I need to transfer some files from my external hard drive to my machine but can't since my external HD doesn't show on my desktop because of the white background.
I reinstalled my OS but the problem continues. I'm thinking that if the problem is still occurring with a fresh OS reinstall, the issue is not with the OS but with some other installed software or possibly a hardware problem of some sort.
Any ideas or suggestions?
I've never before experienced this problem. I've been running OS 10.6.8 for months without problems.

MacBook Pro w/OS 10.6.8

[reader50]

Can you see the menu bar, and/or windows/dialog boxes? Or does the white cover everything?

If it covers everything - do you have an external monitor available? This could be an issue with your built-in display.

Also, you can try booting in Safe mode. During bootup, hold down the shift key. The bootup window should presently update to "Safe Mode" in red, after which you can let go of the shift key. Safe mode disables most system extras.

If the white doesn't cover everything - have you tried another user account? Create a new one if needed, then switch into it. It'll be a blank account. If everything works normally there, then the problem is some customization in your regular account.

[ergo]

Menu bar/windows do show when white screen replaces my desktop. When booting in safe mode white screen still appears.
In new user account there's no white screen; I can set whichever desktop i choose BUT there's no HD icon and I can't make one appear.
In my regular account, after booting up and before the white screen does its thing I can see that there's a HD icon on my desktop which, of course, is then hidden by the white screen and is inaccessible.

[reader50]

In the new account:

Finder menu bar -> Finder -> Preferences -> General tab

As to the old account, it's likely some corrupted preference file or an undesired login item.

Go to System Preferences -> Accounts -> (your account) -> Login Items (tab)

Select anything that looks optional and click the [-] button below to remove it. Then log out and back in to see if that was it.

As to preferences, you can try trashing these files to see if it helps.

~/Library/Preferences/com.apple.desktop.plist
~/Library/Preferences/com.apple.preference.desktopscreeneffect.plist
~/Library/Preferences/com.apple.desktopservices.plist
~/Library/Preferences/com.apple.windowserver.*

Move them to the Trash, but don't empty it. Log out / back in. (if you emptied the trash first, the files might be recreated during logout)

If it works you'll have to reset a few preferences afterwards. You'll likely come up with the default Snow Leopard desktop pic.

[chabig]

Originally Posted by ergo 

I need to transfer some files from my external hard drive to my machine but can't since my external HD doesn't show on my desktop because of the white background.

Drives don't need to show on the desktop to use them. Every Finder window is a portal to your file system, and drives are listed in the sidebar by default. As for your new account, I think the default setting is for hard drives not to appear on the desktop. To change that, Finder Preferences > General.

[ergo]

Originally Posted by reader50 

In the new account:
As to the old account, it's likely some corrupted preference file or an undesired login item.

Go to System Preferences -> Accounts -> (your account) -> Login Items (tab)

Select anything that looks optional and click the [-] button below to remove it. Then log out and back in to see if that was it.

Well, it looks like you pointed me in the right direction. I removed all login items in my admin account and logged in and voila! no more white screen. Dunno which of the login items is the culprit but I'll add them back one at a time and see which causes the white screen, if, in fact, the white screen rears its ugly head again.
Anyway, thanks so much for your help. I owe ya a couple of cold lagers!

[reader50]

Let us know the culprit if you find it. It would be good info for the next person who has this problem.

[ergo]

OK, I found the offending miscreant; it's the screenshot app 'Instantshot'. I also discovered that if I just launch Instantshot the white screen appears.
Funny thing is that I've been using Instantshot for the past year or so without any issues.

[reader50]

Try trashing its preference file.

[ergo]

I deleted my Instantshot installation and redownloaded the app. They've got both a beta update and a stable one....I installed both this time.
Well, whaddya know, both work just fine, without any problems showing.....the white screen issue hasn't reoccurred. Maybe my original installation was corrupted in some way. Anyway, all's well now....fingers crossed.

[luckyguarim]

Solved for me too! I simply clicked on the INSTANTSHOT icon on the menubar and unchecked the "SHOW BACKGROUND WINDOW" and the background return to normal, now i can select whatever BG i want in the preferences. I was looking for this solution on several forums, deleted preferences files, etc, but only this worked. Thanks very much, the background is so important to me, because i put all of my life goals on it! haha = )

all the best