|Consult your motherboard for proper RAM module placement. You should NOT use two different brand/model RAM modules.|
For best results you should use RAM that is one the QVL for your board.
There is a good chance the different RAM modules may have different voltage requirements. That in itself will probably cause problems. At any rate all the specs are most likely different enough to cause problems.
A link to the Asustek site for your motherboard is below. Look at the QVL (Qualified Vendor List) to see if any of your RAM is on there.
Why are you buying RAM off eBay? There are many good online vendors to choose from.
All RAM is NOT created equal. Even RAM that appears to be the same, may not be.