Direct3D application works fine if Windows Explorer is running, it slows down significantly otherwise

Question

The Direct3D9 application works great if we fully launch Windows and then launch it. However, if we select the Windows startup process so that Explorer does not start, and only Windows and our application start, our application slows down a lot. CPU consumption goes up to 50%, even when idle (usually it is about 0).

This can be fixed by launching the Task Manager, launching Windows Explorer and restarting our application. But this is unacceptable; Our application should work without explorer.

Could this be Direct3D? Our application is full-screen, the Windows version is XP SP3 with all the latest updates, and the Direct3D version is 9.0.c. If it is not related to Direct3D, how can I debug this?

Answer 1

I decided. I went to Control Panel->UserAccounts->Change the way users log on or off and saw that "Use the welcome screen" was checked.

Uncheck the box to resolve this issue. It appears that when the welcome screen is active because it uses a different resolution than the desktop, conflicts arise. And I did not check, but it seems that this led to a temporary lack of hardware acceleration and, thus, a software rendering was selected that killed the CPU.