Can't run some games, but can run others

[Space Marine 2 Multiplayer]

So I have a good gaming PC, but when I run these games, it says: "Preparing to launch" but they never really launch. And I played them before.
-Terraria
-Euro Truck Simulator 2
-All Dawn of War 1 games

[Forcen]

https://support.steampowered.com/kb_article.php?ref=6218-USFX-5568&l=

[The Giving One]

"Games do not run after preparing to launch"

https://support.steampowered.com/kb_article.php?ref=6218-USFX-5568

Make sure you also check everything linked there in blue, please.

EDIT..Ninja'd by the good Forcen.

[Space Marine 2 Multiplayer]

Still not working. I disabled all background apps, updates my drivers, verified the game cache and updated windows.
I tried using the installers in the game folders and they say Microsoft Visual C++ is already installed.

[Space Marine 2 Multiplayer]

Verifiying the game cache worked for Euro Truck Sim, but not for the other 2 games.

[Forcen]

Did you use this thing to disable background apps? https://support.steampowered.com/kb_article.php?ref=8043-EUJN-5239

Some more things: https://support.steampowered.com/kb_article.php?ref=5688-IFHZ-2170

if nothing solves it try to make a backup of the steamapps folder then reinstalling steam.
This explains the moving steam thing: https://support.steampowered.com/kb_article.php?ref=7418-YUBN-8129 you can just install it in the same place.

Scan your PC for viruses with your antivirus and malware with http://malwarebytes.org/

If you want to contact steam about this just go here https://help.steampowered.com/en/ while logged in.
search for one of the problematic games and click the right stuff to get to launch issues.
Like this for euro truck:
Home > Games and Applications > Euro Truck Simulator 2 > Gameplay or technical issue
Then you can contact steam support but DONT do this until you tried the things on my first link in this post.

[Space Marine 2 Multiplayer]

OK so Steam was running in compatability mode for Windows 7 and now Terraria works!
But Dawn of War is still not opening, I'll try the other fixes.

[Space Marine 2 Multiplayer]

Alright so I ran Dawn of War in safe mode (using the graphic config file in the game folder) and it worked! Thank you very much.

[GentleMan254 ∞]

could be as simple as restarting steam or even your computer. try reinstalling if restarting steam and your computer doesn;t fix the problem. if that doesnt fix the problem it might have to do with your PC compability with the game

[The Giving One]

Originally posted by Andrei Zago:

Alright so I ran Dawn of War in safe mode (using the graphic config file in the game folder) and it worked! Thank you very much.

This suggests a possible conflict with software that is not launched in safe mode but is in normal boot. Those such as some of the ones found here...

https://support.steampowered.com/kb_article.php?ref=9828-SFLZ-9289

can be suspect. The problem sometimes with certain applications being disabled is that only disables the parent program and not child processes of that parent program that can still conflict.

Antivirus monitoring/updating processes, or backup processes such as Norton Online Backup being examples. And some such as McAfee possibly are even harder to fully uninstall from your system without leaving child processes behind after the parent is uninstalled.