SQL does not exist or access denied

Hello - extreme newbie
Context: I was using some software without problems for the past couple weeks, occasionally it crashed but when started again worked fine without lost data. Today, crashed and would not start.
The error: "Cannot open database TCM. Check database settings or contact your system administrator. [DBNETLIB][ConnectionOpen (Connect()).] SQL Server does not exist or access denied.;clsSBDAO;OpenDataBase, -2147467259"
What I tried: 0) restart computer 1) opened SQL Studio Express 2005 and checked database - looks fine. 2) create new database and restore with backup files - preparing first run --> "Could not connect to server. check that SQL server / MSDE is running and information is correct."
I must resolve this problem as soon as possible.
forest
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