I was having a same problem and since lots of people stumble upon this issue every now and then i guess it won't hurt to post my solutions.
I was modifying my visual style and ended up messing up the shell32.dll, and next time i restarted the machine the atbroker.exe problem appear.
The logon screen was normal but when i logged in it was just black screen. I tried to logged using safe mode but the problem persisted. Task manager wasn't working, no luck in system restore too.
The solution is log in using Safe Mode with command prompt. When the command prompt loaded, type "sfc/scannow" without the quotation mark and wait until the scan complete. After that, restart the computer by typing "shutdown -r -t 00" without the quotation mark.
Works for me.