Ran Windows update (yes, there was one needed, but no .NET update). Did not resolve or modify the problem. But thanks for that suggestion, to at least rule out one possible source. I did check the Windows Event Viewer, and see some security events that seem to correspond to my attempts to open Tequila/CoH, but the event codes I get, 4672 and 4624, don't give me enough information to figure out what's happening (barely computer-literate). Many thanks for taking the time to answer, regardless.