That is baffling, maybe you need to run matched pairs like I said before, so sticking only the 8gb stick in or an 8gb and a 2gb stick is tripping it out.
You might need to buy another same 8gb stick.
Was the 8gb stick brand new or 2nd hand?
Brand new.
Yeah, bizarrely I haven't tried the 8gb stick on it's own. Oops. Will try that tonight.
Cheers!