Sims 3 Strange Error

Backstory: I had originally had the Sims 3 base game installed with Steam. I still have the Steam program installed for other games I have. I have deleted the Steam version.

So, I have a strange error message that states "Uninstallation cannot continue because programs associated with The Sims 3. Please stop these applications before attempting to uninstall The Sims 3" 

Side note: When I mounted The_Sims_3_Startdisc.iso I selected 1 drive because I have watched a bunch of tutorials on YouTube, and they always selected 1 drive.

Hopefully by "deleting the steam version" of the Sims 3 you mean you uninstalled it, not just deleted the Steam folder. If so then try these steps:

1. Make sure Steam is not running
2. Insert/Mount the install disk and install the game
3. Update to latest patch level either through the launcher or by using the Manual Patch
4. Apply the Ultimate Fix making sure to folllow the directions.

What I have here, is my Steam account says Sims 3 is uninstalled, I logged out of my Steam account, thinking that would stop Steam from running. I am still getting the error message.

I also just tried running the setup wizard directly from PowerISO, and I have another weird error message. It says,
">SetupNew\setup.cpp(140) 
PAPP:
PVENDER:
PGUID:
$15.0.0.498
@Windows Vista Pack1 (7601)
IE Version 9.10.9200.16686"

You have to stop Steam from the system tray as well. Right click on Steams icon in the system tray and select quit/exit

I have done that. Multiple times. I even thought maybe Origin was the problem, so I uninstalled that as well.

Thinking that I might have shut down Steam improperly, I uninstalled Steam. I am still having the same issues.

Have you tried perhaps opening task manager and ending the process steam.exe? Theoretically it shouldn't still be running, but steam is a slippery little program.