Program Compatibility Assistant will give you warnings or even wont allow you to run known incompatible software.
The problem is that some software (like classic shell) will work fine except some minor problems that can be avioded.
Here is a guide to Disable Program Compatibility Assistant and run your software. Keep in mind that you must know what you are doing and what software you run. Incompatible software can really make yous system even not bootable!.
Step 1: Stop and Disable Program Compatibility Assistant Service
click Windows Button + R to open run window, type there ‘services.msc’ and click OK
Find Program Compatibility Assistant Service and duble click on it.
On ‘Startup Type’ click ‘Disabled’ and click ‘Stop’ button the ‘Apply’.
Step 2: Disable Program Compatibility Assistant from Group Policy Editor
Once again click your Windows key button + R to open run window.
Type ‘gpedit.msc‘ and OK. Group Policy Editor windows will open, navigate from left category folders to:
‘Computer Configuration, Administrative Templates, Windows Components, and Application Compatibility’
and enable (by double clicking and clicking ‘Enable’) the
‘Turn off Program Compatibility Assistant’ and ‘Turn off Program Compatibility Engine’.
Step 3: Reboot and rename your executabe file.