Check these 2 :-
1) SLI Bridge
Is the bridge used to connect the 2 cards. A SLI bridge should be supplied with your motherboard. If it is inserted already, take it out and reinsert it again to make sure it is totally fit in.
2) Power supply
Each GTX560 Ti needs two 6-Pin PCIE power connectors. So, for two cards, you need a total of four. Make sure all four are plugged into the cards.
I am not sure which Rosewill 630W PSU yours is but the two models listed in Newegg both say they have only one 6-Pin and one 6+2 Pin. This means, you will need to use a pair of 'two 4-Pin Molex to one 6-Pin PCIE' adapters. Are you using these?