Windows 7: Programs fail to start

I tried Win 8 but had problems with Flight Simulator so returned to Win 7. Since doing a clean re-install of 7 I've had issues with programs failing to start for one reason or another. Live Mail for example will run fine for a few days and then suddenly will not run giving the message "the version of this file is not compatible with the version of windows you are running......etc"
Flight simulator also runs and then will give a "errorID=24 (null)" message.
Any ideas?

I know your post says you did a clean reinstall, but just to satisfy myself, did you use the procedure in the link below;

Clean Install Windows 7

Make sure you followed the Best Practices for Windows 7 install given in Clean Reinstall - Factory OEM Windows 7 which are the same for retail. By sticking with the tools and methods given you will be assured of a perfect install going forward.

Most importantly use only the drivers given by the installer and delivered by WIndows Updates (under Optional), making sure Updates are set to Automatic and all fully installed - including Net Framework 4 and all of it's attendant Updates. Automatically get recommended drivers and updates for your hardware

If problems then present themselves work through the Troubleshooting Steps for Windows 7 checking the logs for repeat errors to resolve, establishing a Clean Boot, utilzing the System Resources to find solutions to problems.

If anything catches your attention post it back for further help, or google error messages verbatim to learn how others have resolved them.

I thought i'd done an OK install by formatting the drives before installing. I used exactly the same procedures as i have previously which had an OK OS for the last couple of years! I'm assuming this is a registry thing?
Looks like another install and 8 hours of automatic updates!!!
Will keep you posted. Thanks for the assist.

It will be less than an hour of updates providing you use the latest official installer in Step 1 of Clean Reinstall - Factory OEM Windows 7.

If you follow the steps to get it perfect, then after it's setup and running fine save a Windows 7 backup image so you never have to reinstall again - just reimage the HD in 20 minutes from the DVD and stored image.