David,
I am using a newer computer. The problem is it won’t guide on a star. The star won’t stay on the slit. Guiding instrument is a Lodestar Pro. If by calibrating the system you mean guide assistant it says there are mount backlash issues which it recommended corrections for. As a test when trying to guide on Vega it won’t stay on the slit.
So far it appears to point to a problem with the mount.
Jack
British Astronomical Association
Supporting amateur astronomers since 1890