Community Tip - You can change your system assigned username to something more personal in your community settings. X
If it points you to check the log files, it'll also tell you where they are.
What does it tell you?
Maybe a screenshot...?
And of course, you can have a look here: https://community.ptc.com/t5/PTC-Mathcad-Installation/All-About-Mathcad-Software-Installation/td-p/706433 to see if there's some information that can help you solve your problem.
Success!
Luc