I am glad to hear it worked, but you also want to be careful that you can actually use that much memory. I have no doubt you were fine with the amount you had, but I have often seen (usually with older boards) where there is 3 or 4 slots, but a max memory addressable of only 2 GB. You have to look at the board manufacturer's manual to see what (and in what order) to place the memory. With older (pre-DDR) boards, there were often 3 slots that may have a max size configuration of 1gb in slot 0, 512mb in slot 1, and 512mb in slot 2. I haven't seen DDR boards in any strange configurations, but I wouldn't rule it out. Everything I have seen so far would be something like max 1gb/slot or 2gb/slot. However, I could imagine situations where it might be a matched pair 2gb chips in the first pair slot and 1gb chips in the second pair slot for a max capacity of 6gb.
Other good troubleshooting techniques include swapping memory in the slot to determine if one or more chips are bad, and swapping the configuration to see if the slot is bad - but by the sounds of it, that is what you did. One last good thing to do if you suspect bad chips and you want to test it for certain (assuming you don't have issues that force you to determine the issues through beep-codes), you can use Memtest++. This is a very good and very small program that you boot into and it will run several tests on every memory address in every chip that the motherboard recognizes. All you need is one good chip plugged into the motherboard for it to load the program into memory. The program will test them all after that.