I built my system a couple of months back with the specs listed at the bottom of this post. Since the beginning, it would lock up once a day. I haven't had time to deal with it, and it's been getting worse and worse. It never generates any kind of error message. The most common scenario is that I'll come to the locked computer and the time it's showing is way behind. It'll let me log in and go maybe a couple screens before it stops responding entirely. The other common issue is I'll be watching a video and the sound will basically start stuttering like a scratched CD, and it never recovers from it, even though I can usually switch between windows for a little while.
I've tried using each of my sticks of ram alone and had the same issue. It was also happening before I installed the graphics card, so I'm assuming that's not the issue. It doesn't seem to be software, because it happens even when I haven't logged in. I'm guessing it's the motherboard, I'm just hoping it's not or is something where I won't have to send it in, since that's going to be a real pain.
Corsair Obsidian 650D
MSI Z68A-GD55 (G3) Bios v. 23.7
Corsair TX750 V2 PSU
Intel Pentium G620
CORSAIR Vengeance 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)
Samsung 830-Series MZ-7PC128B/WW 128GB SATA III MLC Internal SSD
EVGA GeForce GTX 560 Ti