Try this first:
Right click on desktop and click properties and go to Desktop Tab and change your desktop backround to one you know you used before or another one that is listed and click apply and restart to see fi this gets rid of it.
If that does not help, try a system restore point to go back to a date and time this was not happening.
Use System Restore
After you've decided to use System Restore to revert your system to a previous state, start the System Restore Wizard and follow the prompts. To use the System Restore Wizard, make sure you're logged on as an administrator, and then follow these steps:
1.Click Start, point to All Programs, point to Accessories, point to System Tools, and then click System Restore.
2.On the Welcome screen, click Restore my computer to an earlier time, and then click Next.
3.On the Select a Restore Point page, select the date from the calendar that shows the point you'd like to restore to, as shown in Figure 2, and then click Next.
4.On the Confirm Restore Point Selection page, verify that the correct restore point is chosen, and then close any open programs.
5.Click Next if you are ready to proceed or click Back to change the restore point.
6.The computer will shut down automatically and reboot. On reboot, you'll see the Restoration Complete page, and then click OK.
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