Sian: Apologies for taking a while to reply. I've tried the Moodle Windows Installer package out on a test PC and I think the problem might be that you need to download and install the vc_redist.x86.exe link for the Microsoft Visual C++ 2015 Redistributable package (not vc_redist.x64.exe although it won't cause a problem if you've done this).
Installing and upgrading help
3.4.2 New Installation php.intl.dll will not load
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