It would be normal for your computer not to boot if you only had the ram in the second slot. The first slot is the motherboards base memory. And if you swapped the chips and it worked fine then the ram isn't bad. I would check for any BIOS updates for your motherboard first.
Second, does the computer feel like it runs faster? Is there a noticeable difference performance wise? If you see a difference then just go with it. Windows/ BIOS can't properly detect the new memory but addresses it anyways.