Which one is the only one that's working - which slot and which stick? Can you move them around, like swap places 1 and 2 and see what happens.
Reseat the sticks anyway, good to try anyway lol
There's a BIOS option called XMP, try turning it on/off and see what happens.
If none of those work - plug it all off, take the CMOS battery (looks like a watch battery, inside the case), hold the power button with the power off for an extra power cycle and put the battery back in and plug it back in. This will reset BIOS settings back to normal, you might have a confused clock when you boot up but it should be fine.