Cydia won't open after ios 6.1.3 jailbreak?

I recently jail broke my iPhone 4 with redsn0w, it is running ios 6.1.3, when i try to open cydia the screen flashes and nothing happens, i tried it about 5 times

You've to boot it in the tethered mode for the jailbreak to work. Open Redsn0w again, go to extras and click on the "Just Boot" button. Follow the procedure. Since its a tethered jailbreak you always have to do it after restarting your device.