the timing of your new memory

module is set incorrectly in the cmos setup.
1) try use the new module only (pull out the old one), set the cmos accordingly, see if problems happen.
2) compare the new and original timing settings, set the cmos to the slowest one, put the old memory module back in.

I am pretty sure the issue is caused by the timing incompatibility of two memory modules. The point is to set the timing in the cmos to the slower one, so both can work.