Maybe you're having the same problem I've reported in issue 794934?

If you write "bug 794934" instead of issue, you get a link. ;-)

Can you try to move the file
c:\Users\<your-username>\AppData\Roaming\GnuCash\stylesheets-2.0 out of that directory and try to run gnucash again ? That would confirm the issue to be similar to the one in bug 794934 or not. It may be it now crashes while trying to load saved reports, in which case the saved-reports-xyz file(s) need(s) to be moved aside as well.

Does your windows user name contain non-ascii characters like accented characters (é, à, ö, ç,...) ?

Nobody here provided a trace file or similar.
I watched in bug 794934 they were using Microsofts Codepage 1252.
In that case, can you change it e.g. in your Sytem Settings to UTF-8?

There's a nightly build at https://wiki.gnucash.org/builds/win32/maint/gnucash-3.0-2018-04-16-git-3.0-75-g87f94abc8+.setup.exe that includes a change to converting characters from Scheme to UTF8 that I think resolves this issue. Please test it.

The nightly build in the comment above won't run due to a missing dll. I have just now created a new installer to fix that:
https://wiki.gnucash.org/builds/win32/maint/gnucash-3.0-2018-04-17-git-3.0-75-g87f94abc8+.setup.exe
Please test with that one and report back.

I have tried the new installer from comment 6 and it works without any trouble. The installation was completely straightforward. The new GnuCash looks very good. Thank you for all for such a great program.

Another User has also tried the Version from Geert in Comment 6 and reports it to work without Problems.

GnuCash bug tracking has moved to a new Bugzilla host. This bug has been copied to https://bugs.gnucash.org/show_bug.cgi?id=795009. Please update any external references or bookmarks.