i can't set any theme or background it's always black screen or any other color i don't know what i have to do

Which Windows 7 Edition do you use?"A programmer is just a tool which converts caffeine into code" CLIP- Stellvertreter http://www.winvistaside.de/

i use windows 7 ultimate

Right click desktop. Go to personalization. Click on desktop background (should be on left under the black square that is your desktop color). Another page will open and will be a drop down menu for you to choose what you want for a background. (menu should be above a lot of color blocks). Make sure you hit save changes when done.

it's not working nothing can make it changes

Try going to control panel. Then system. Then click on Performance information and tools. (should be on bottom left). Then on next screen click on re-run assessment. (should be on bottom right). This will take a few minutes. Hopefully it helps.

It dosen't help too

check if you are getting windows not genuine message on your desktop. If so, you cant change! http://www.microsoft.com/genuine/

it's genuine but not activated

activate it.. then only u can set any theme or background