Usually problems like this are not caused by dirty DIMM banks. Try putting one of your old modules in slot 1, and then a new one in slot 2, and then memtesting the whole thing. You can find memtest from
http://memtest86.org. Just burn the ISO to a CD with something like IMGBURN, and let it run for a couple of hours. See what you get.
If it still can't boot, my guess is that your ram is not compatable with your board. You can use Crucial's excellent scaning tool to see what type of ram you should have.
http://www.crucial.com/Billy3