mac12

Hi guys ive recently bought a new pc in order to go to university. The plan was to buy the pc pre made but to add in a gpu to replace the integrated graphics card. Being a computer nooby i originally thought (because the inside looked different to my old system) that my GPU (ATI 5770) wasn't compatible with the motherboard so i gave up. Then last night i had another look and found that with some difficulty the gpu does slot into the motherboard. My problem now lies upon looking at the connections from the current power supply. from what i see there are 2 sata cables, one going into what i percieve as the harddrive, and the other the cd drive (not certain but fairly sure) The power supply needed to run my gpu however only has one sata so i was wondering if: 1. i should just connect the sata to the most appropriate place (advice please) and 2. if i plug in the sata in one place and not the other with the other not have any power to function? the rig i have just bought is HP G5210uk at cheap prices | PC World Please if ive missed any info out just ask i will give as much detail as possible as i have here. if im being stupid let me know nicely, as i said im at a very beginner level with computers but looking to improve.