sounds like you did not reset the bios or change the values in the bios. it might be still using the old config for the memory and not optimized for the new memory you bought.

best thing to do is enter the bios and manually change the memory desired config that the memory is set to run at (speed, timings, voltage, etc) on the package.

or you can just load "optimized defaults" for the bios, this will erase whatever settings it has in there and load the default for the board. then it should detect your hardware and what not. note this will erase whatever settings you set in the bios, so if you overclocked you will have to reenter those settings again.

another thing is to get memtest+ and test the memory one-by-one to see if there are errors, this of coarse is after you set the correct memory info into the bios and save it