Hello,
Helped my buddy assemble his first rig, very exciting, but also very disappointing when the PC would only boot with 1 stick of RAM. Here are the steps I took in determining that it's probably a MOBO issue.
1. Removed graphics card w/ both sticks still installed - all lights and fans on, but still no post
2. Removed RAM from DIMM 2, posted, booted into BIOS, then proceeded installing windows etc.
3. Updated BIOS for MOBO then added second stick back - no boot
4. Installed graphics card back with only 1 stick of RAM - booted fine.
5. Installed 2nd DIMM again w/ gfx card - no boot (should be noted that graphics card fans spun briefly then stopped, but never started back up again).
6. Pulled the 2 sticks from my other rig, and installed, and got the same results with both 1 and 2 sticks installed.
To get the basic questions out of the way, I did use the gpu outputs when it was installed, and used the MOBO outlets when not installed. I also switched between VGA and DVI. I used Crimson utility to update drivers for graphics the gpu also. The sticks of RAM were firmly seated when installed, and both clips snapped firmly into position. Additionally, all fans connected to the PSU and MOBO, including the CPU fan, spun up and maintained speed after power-on even when there was no post.
I could find no options outside of the "overclocking" menu on this MOBO to change memory speed. This is a relatively cheap-o build, so fair warning before looking at the hardware. He is using it right now for low-demand games like WoW and Smite, but may run into problems on some more demanding titles with only 4 gigs of RAM. Let me know if you have any questions, and all help from the community would be greatly appreciated. I do have another MOBO on-hand, but I'd rather not open it unless I've exhausted all troubleshooting options for this one.
Hardware:
MOBO - MSI H81M-P33
CPU - i5-4590
RAM - G.SKILL Ares Series 8GB (2 x 4GB) 240-Pin SDRAM DDR3 1600
SSD - Silicon Power 120GB S60
HDD - WD Blue 1TB Desktop Hard Disk Drive - 7200 RPM
Monitor - Acer G236HL Bbd 23-Inch Screen LED-Lit
GPU - MSI R9-270 Gaming
Case - Rosewill Gaming ATX Mid Tower Computer Case Challenger S
PSU - EVGA 500 W1 80+