The sliding switch on the back is there to provide for using the computer with either 115 Volts OR 230 volts. If your normal house current is 115/120 you should leave the switch at that setting only.
You might try unplugging and then replugging the Power Cord into the back of the machine.....AND do the same at the wall plug...AND/OR temporarily Bypass your Surge Protector/Battery Backup, to eliminate that as the possible problem.
This problem occassionaly happens to me and I have NOT found the cause yet. Plugging/Unplugging usually does the trick until next time..which may be weeks or months. The next time it happens to me I'm going to open the box and Reseat all the Cards, Memory Modules, cables, and plugs inside.
To do this requires you to unplug EVERYTHING from the back of the computer and I'm lazy, so that's why I havn't done it yet.. John
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1986 Minx. SBC 350/260hp, Alpha I. Red, Honey.