[dba-SQLServer] Backtracking installations

I have no idea what is going on, or what is failing to go on. All I'm
thinking about at this point is to un-install erverything concerning SQL
Server (all versions included), and then reboot. clean the registry, and
start again. Furthest I want to go back is SQL 2008 R2; atop that, SQL 2012
Express, then (hopefully) re-attach the dbs that I already have residing on
a separate hard disk.

Any guidelines before I attempt this radical surgery?

All of this is Dev not Test nor Production. Just want to get the basics
working again.

TIA,
Arthur

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Cell: 647.710.1314

Prediction is difficult, especially of the future.