I own an MSI P7N Platinum board. This morning I installed 2GB of memory into my board, giving me a total of 4GB. I booted up into the BIOS and noticed it only recognized 3GB. So I went in and resat the memory and still I come up with 3 gigs. Then I thought well...maybe a stick is DOA? So I tried each stick in one slot and they all worked fine. This made me realize that one of the memory slots is fried. Now my question is, is they're any way to fix the slot without sending my board back to MSI? It's just going to be a pain to take it out then ship it back and wait for a replacement.
Did you enable memory remapping in the BIOS?
The BIOS should detect the 4 gig, once you boot into Windows however, that is a different story. A 32 bit OS will not be able to use all 4 gig of your main memory. It can address 4 gig, but that is the total memory counting ALL the memory in the system (video cards, hard drive cache, processor cache, etc.) It will address these items space first, and whatever is left over will be addressed for main memory. Depending on what else you have in the system, most people end up with around 3 gig of useable memory.
Was there lots of dust in the slots? If so you could power down and take out the sticks. Then use an old toothe brush or similar and brush out the slots with a little contact cleaner.
Are you using all 4 slots or just 2? Some boards don't like using all 4 slots!
Also check your vram OCZ is usually 2.1volts.
If no luck then you might be facing an RMA.
You could also take back the 4 sticks of 1GB ram and get 2 2GB sticks.
Hope this helps