I have 1 sata 2 cable and i need to power a r9 270 whats the best way to go about it without buying a new PSU?
I'm not quite sure I understand what you are asking. There is no such thing as a SATA 2 cable. All SATA cables are the same. The SATA cable does not power the graphics card, it simply sends and receives data.
The R9 270 requires a single 6 pin PCI-E power connector to power it. It looks like the image on the left (below). If you don't have one, you can convert 2 4pin connectors to a 6 pin (right hand image). Warning: make sure your PSU can handle the power requirements if using an adapter.