When attaching the 2 plugs (P8 and P9) from the power supply to the motherboard, ensure that you do that correctly, because it is possible (with force) to attach them to the wrong receptacles (i.e. P8/P9 swapped).
Do not worry if your P8 is missing the red wire (next to the orange wire) shown in the photo. My power supply (a clone one) has that wire because it's designed for ATs (as well as PCs and XTs).
As specified above, on the motherboard, switches 5 and 6 on SW1 are both to be set to the OFF position (monochrome card). For this procedure, that is very important.
Actually, either 5 or 6 can be ON, but not both. For simplicity, I'm saying to set both 5 and 6 to OFF (per the switch photo).
On a 5150 motherboard, there are 2 switch blocks: SW1 and SW2. SW1 is the one closest to the center of the motherboard.