Keyboard connector does not fit into keyboard port due to wrong size.

Cause:

There are 2 sizes of keyboard connectors that dominate the market today: the older, larger 15-pin connector and the newer, smaller PS/2 style connector.

PS/2 Style Keyboard and Mouse connectors

Solution:

If newer keyboard has both connectors, try the other one. If not, obtain an adapter plug to connect the two (be sure to specify which direction).