I have the ASUS M5A97 and, and my case is the Ostrog eca3250. My case came with a single (4 pin?) molex fan and I was wondering how to connect it with my motherboard, thank you.
You can't directly connect it to a motherboard.
With a molex to 3 pin adapter, you could, but the fan will have no speed sensing so you might as well connect it directly to a molex from the psu.