My PC has Hyper X Fury 8gb 2400mhz and I have an extra Hyper X Fury 8gb 2133mhz. My PC wont boot when I installed my 2133mhz Hyper X Fury.how did you try to "downgrade"?
set 2133MHz in BIOS
eventually reset BIOS by jumper
Thank you for this...In which slot did you install the new RAM?
the motherboard wants to boot 2400MHz, but your 2133MHz RAM crashes, so you will have to reset the BIOS of your motherboard by jumper, so the motherboard can boot with only 2133MHz with both modules.
How to clear the CMOS is usually described in the motherboard´s manual. Jumper = two pins shortened while power is off