I had this problem on a vintage 286... (that was LONG ago).
There were 2 keyboards for 3 computers, so there was swapping
all the time. Eventually, the 286 had the keyboard connector
broken (it looked normal, but there wasn't any contact between
one of the connector's legs to the mobo)... the problems were
exactly as you described "won't boot, no keyboard" type.
  That was the end of that 286... :(

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