Hey, I had an experience last night that wasn't very good, but it was resolved. I hope this helps you.
I downloaded a Windows 7 theme while I'm running a Windows 8.0 OS, (Yeah, I know, I'm stupid.) and realized I had no access to my desktop, but with some knowledge I was able to revert to a previous date. Here you go.
Press CTRL+ALT+Del simultaneously. Open Task Manager. The window should look something like this.
Notice that "File" tab? Click it, then "Run new task".
Make sure to open this program with administrative privelages: msconfig
Now you'll have a window that looks like this -
Advance to the Tools tab, and scroll down. You should see "System Restore". Click Launch. Follow the wizard, choose your date, and you'll be able to have your working desktop back.
