Testing can be done with Memtest, or similar. Assuming that you can get them to work one at a time, as per previous post.
Unlikely to get 2 failures - too much coincidence.
I have had motherboard problems where 2 x 1GB modules were supposed to be supported (as per manual), but actually weren't - admitted on Asus support forum. Worked fine on their own, just not together. Asus couldn't give a sh1t.
SD