I had a very similar issue My 2TB HDD always had errors that chkdsk needed to resolve games crashing! Getting BSOD somethings occasionally random restarts without any BSOD and hard crashes sometimes.
I resolved my issues with tuning the RAM Timings!
You have said you changed the RAM so its a strange case with your system!
But try to tune the RAM!
If that doesn't solve it and you have tried everything then its the motherboard but im 90% sure its the RAM.