There is a free evaluation -- a limited form of the software -- no saving of files. There is no time limit - you can use it solely as a viewer for other files.
Try rebooting your system. PCStitch 11 is the version that "officially" supports Win 10. The only difference between the trial version and the purchased version is the "unlock code".
What is happening? Are you getting messages?
If you continue to have problems, I suggest you contact Mark at mmiller@pcstitch.com with as much information as you have on the issue.
I finally got the program installed. Now to play around with it. Does it work in any way like Pattern Designer? i.e. keeping track of stitches? Sorry to be such a pain.