Some motherboards can be particular about ram brands.
It's not just about changing sticks, but sometimes changing manufacturers can be problematic.
If the 2 gig is a pair of sticks....try each one only....and in different slots.
Are both the old and new the same 'speed' and type?
There are particularly 2 parts of a computer that are delicate....ram and cpu .... both can suffer severely from static discharge, and/or soiled contacts [through skin oil].