Do you use RAM of different kinds or purchased separately? For GSKILL, if modules are made in different years, they won't allow you to boot up without MemOK's help. Use CPU-Z. Mine shows my newly purchased modules (of the same exact type memory model...
Unplug power. Hold power button down on PC case for a couple of minutes. Plug power back on, power up PC, look at device manager. Unknown device now has a name and you can install a driver.