If you have problems with TaxAct on Windows 10, you may need to check your security software or any Windows 10 security (firewall, user account control, Microsoft security, Windows Defender) to make sure it is not interfering with installation or program operation. You can change settings or temporarily disable the security (you will need to consult information for whichever security for how to do that). If you upgraded from an older version of Windows to Windows 10, you may need to re-install the software if you did not do so after upgrade.
You can try running the program as administrator. Right-click the program shortcut on the desktop (or icon from wherever you run the program), then click Run as administrator from the pop-up menu.
If you are able to run as administrator, this may mean there is an issue with the rights of the Windows user account you log in with, or that the program no longer has rights for all user accounts. You would need to consult Microsoft help for how the upgrade may have affected this and how to allow the program to run for all users (see note below). This may also be due to security software or Windows Defender.
If running as administrator doesn't work, try the following:
Note. When upgrading to Windows 10, you may have, even inadvertently, transferred your user account to a Microsoft network account. If you had a local user account on the OS before, upgrading to Windows 10 may not bring the same permissions if you switch to a Microsoft account. The best way to avoid permissions problems is to use a local account, though even then you may need to be sure you have the same permissions, or administrative rights, after upgrading. For any user account that was in a network work environment, in an office for example, you may need to consult the system administrator.