This happened to me me when i first built my rig. the only way i got it to notice both and then put it in sli was 1. have only one card in and install the latest drivers 2.then turned it off and plugg in the other card (with out sli ribbon)<--this was to test and see if it saw i had a 2nd gtx if it does not see it 2nd gtx, switch the cards. like if the Asus card is in the 1st PCI-e port and the galaxy in the 2nd PCI-e port, switch them. Yes it sound stupid but it worked for me, so. 3. connected the two cards with the sli ribbon this is the only way i got my sli config to work. hope it helps