is this new memory ? does your old memory work ? are you using a ''K'' cpu ?
''Don't know if I did it right, I plugged in PSU, turned PSU on, then pressed clear cmos''
should be all covered in your boards manual
pages 35 - 41
https://www.manualslib.com/manual/438973/Asrock-Z77-Extreme4.html?page=43#manual
see on page 43 it shows that dr debug code 55 is memory NOT INSTALLED . be sure your inserting it in there slots correctly and its firmly locked in place [page 20 ]
then I googled that CMZ8GX3MA1866C9B. you must be missing a number in that part number should be a 1 [single stick - 2 [ 2 stick kit] -4 [4 stick''] or 8 . CMZ4GX3M ''2'' A1600C9B = a 2 stick kit for example
so I don't know what to tell you on that deal
I'd check at corsairs site and see if its real corsair memory or some kind of bootleg
http://www.corsair.com/en-us/memory
if it still fails you back on the memory you were using and these sticks got a problem and I guess try another 1866 kit if needed ?
did you buy this memory new ?? cause then 1866 memory from corsair seems only to come in kits not sold a s single ?? [best I see form them ]