1. Switch off your PSU.
2. Disconnect the power cable.
3. Remove all your RAM.
4. Remove the CMOS battery for 5 minutes.
5. Put the battery back into place.
6. Reconnect the power cable.
7. Switch on your PSU.
8. Insert one stick of RAM into the DIMM_A2 slot.
9. Power on your system.
If all goes well, you should be able to post and notice that your RAM is running at 1333MHz. Proceed to setting it up to run at 2400MHz eitherusing XMP or doing it manually. I'd recommend manually. When you're done, save and shutdown your system.
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Went fine till here, changed the memory frequency to 2400 Mhz and was successfully able to post and get into windows
adding the other RAM to slot B2, didn't post, did not post error code 55
swapped RAM between a2 with b2, error code 55
just had the working RAM (i believe) in B2, posts successfully.
I had also done another check previously before the steps you've shared, had the working 8 GB RAM in B2 and a 2 GB RAM in A2 was able to post with clck 1333 Mhz