First, no need to triple post.
Second, verify that you have downloaded the correct version
Third, try reinstalling from scratch, verify that you have administrator privileges and AC is closed. Uninstall AC and make sure that you remove the folder from "Program Files" then do a restart. If everything fails download the student version of AC11 and install it to see if it works.
Third, please put your system info in your signature. For example AC10 is not recommended for Vista.
Last, even though it seems that the end of the world putting URGENT in front of your post does not make it more urgent. In combination with the triple post it makes it more unlikely that your problem will be taken seriously.
Eduardo Rolón AIA NCARB
AC27 US/INT -> AC08Macbook Pro M1 Max 64GB ram, OS X 10.XX latest
another Moderator