I thought I'd go ahead and post this.   I decided last week to put together some old parts I had laying around to make a PC for the Garage to listen to music, look at woodworking schematics, car schematics, whatever for internet purposes.
 
I put my 790i in that I retired a few months ago.  It has a qx9770.    I took photos of all the bios settings before I disassembles and pretty much left them in place.   After everything was set up and after trying two different power supplies and two different video cards,  I discovered black flickering in the OS when I put in the memory stock settings.   It's supertalent project X 2x2 gm    8,8,8,24 2T.     Tried both pairs of slots on the motherboard.   I memtested the set on a boot CD and it passed 6 full tests.   
 
But when in the OS, at 1800 speed, flickering occurs.   CPU has been prime tested stabile.     Memory is memtest tested as stabile.  
 
So, If I back the memory off to 1333, all problems go away.    Which is fine for 24/7 internet usage, which is all I am basically using the setup for.    I'm ok leaving the memory there but wonder if there's any suggestion as to why the memory won't run at 1800 speed.   Voltage is set correctly as to factory spec.   I have disabled the profile and manually put everything in.   I know this is an old board, but it works great for purpose of just internet use.
 
Part of me says leave it as 1333 vs 1800 won't make mush a difference in browsing and it's stabile.  But the overclocker in me can't let it go.   
 
 
any ideas?
 
build has:
 
GTX 280  (also tried a GTX275 I had laying around)
790i ultra with QX9770
supertalent project x 1800 2x2gb   8.8.8.24 2T

running 3.8 ghz.   multiplier 9 FSB is 1700.  Memory defaults to 1700 even though you put in 1800 manually.  But yeah, I tried manually entering 1700 to match the FSB as well and the OS still flashes.   I have tried old and new drivers, so I don't think that's an issue.  
 
the 3.8 ghz passes prime 95 small fft.    Do you think that the memory controller in the cpu is just tired and will no longer handle higher frequencies?
 
and yes, everything was cool before.  It least I didn't notice any instability.  but I'm running a new SSD, so I reinstalled the OS on a different disk. But I don't think it's the SSD. 

that's right.  it is on the northbridge.  Forgot about that.  I did try manipulating those voltages.  Tried auto and 1.45.   Seems to be what the were.  I am not sure about the bios.   I know there's a way to do it via USB but I don't have any CDr to make a bios boot cd.   I did try with a DVDr but the old dvd rom drive i'm using didn't like the media.   I think it's current.  I kept those up to date.    P1 P2 have been on auto.   It's stabile at 1333.  So I guess I'll leave it there.  I do have another exact set of RAM I could try.  I have two of those boards. One is a server now and the other I have in the garage.    I could try the other set of dimms to make sure I just don't have a bad set.  Thanks for your ideas..   
 
Trying P1 P2 enabled now an so far so good.  I'll put it through the paces to see if the flickering come back. 

I will check on the bios.   enabling p1 and p2 made a difference.   It's now stabile at 1700.  Passed 14 passes of memtest last night and prime 95 small fft.  So flickering has stopped but I get an occasional black background to the windows in windows 10.  I am going to try a different monitor and cable but otherwise call it good.  symptoms were the same with both identical sets of ddr3, so I don't believe it's the RAM modules as being bad.   The P1 P2 was on auto and now enabled and I boosted SPP to 1.4 volts.   

I think you need to set Voltage of Memory dimm  up to 1.55V(or more). You may get a stable CPU OC. Because 790i Still work with NorthBridge that make CPU and Memory tjo Work Simualtaneouslly.