1. 32-bit OS can have a max of 3.5, assuming you have a pretty weak (for modern times) graphics card, so that is not an issue.
2. Can you check all memory sticks to verify all of them work fine? Like, put one, then get the first one out and put another one, and so on; then 2 sticks, then 4 (in case there are 4 sticks)
3. Is your motherboard new? Works good? Can you check the memory on another computer?
Seems to me, it's a problem related to your hardware, not software.