A bit confused ...

I guess you bought a Dell PC with XP Home preinstalled and later upgraded it to XP Pro with a reatil CD, right?

Can you run system restore %SystemRoot%\System32\restore\rstrui.exe to roll back?

Can you tell me the nature of your C++ program? What harm it could do to your system? Deleting files, changing registry, kernel level driver?

What happened when you ran explorer.exe from Task Manager?