Graphics card causing black screen and crashes

My specs are:
CPU- Intel Core i5-6500 3.2GHz
GPU- Sapphire Nitro+ RX480 8GB
RAM- Corsair LPX Vengeance 8GB 2666MHz
MoBo- Gigabyte G1 Sniper B7 B150
PSU- Corsair CX500W
The problem continued when i played Titanfall 2. Whenever I played it for a while it stuck and the monitor went to sleep (The display was not getting signal from HDMI). Again whenever i played again one night, it was working fine. And again the problem persisted. And i tried to overclock it to max settings (On Sapphire Trixx Kit). And it showed some glitchy effect on screen sometimes green screen or BSOD. And I played Need For Speed and Payback, Rainbow Six Siege, Watch Dogs on low settings. It lasted for a while after that the monitor went to sleep again. But it didnt exist on Watch Dogs 2 on ultra settings. And now i play Farcry 5 on ultra and low settings but it still crashes on startup or sometimes goes to sleep. I tried to run with another psu, same problem persisted. I flashed and updated my mobo bios. Now what should i do to find out this problem? (Sorry for my bad english). I am running Windows 10 latest build.