Macbook pro 13 2012 (HD4000) 8GB(1600 Mhz) single RAM stick issue I have a Apple Macbook Pro 13" 2012 IvyBridge HD4000 Model which came with
2GB x 2GB RAM.
I Recently bought a single stick of 8GB RAM 1600Mhz (which is compatible).
Gskill 8GB DDR3 FA-1600C11S-8GSQ Notebook Memory for Apple Mac
http://techshop.in/store/product_info.php?products_id=10064.

I removed both the old RAM DIMM's and placed the New 8GB RAM in upper slot and lower slot but when i boot the system after a few seconds or minutes the display gets 
distorted and system does not respond and have to hard boot.

Is it because i'm using only one stick?
Do i need to buy another same kind of 8GB stick to make it work...

Please help.
It could be the RAM is just bad. It happens sometimes.

But try to rule this out. Reset SMC and NVRAM(why not?) and boot into Apple Hardware Test to check the memory.

Also you may try to use new 8GB stick paired with old working stick. If it will be OK than don't try to buy same second 8GB stick it will not work. Though it does mean you can use this module with different fully compatible one it's better to send it back.

Anyway I would recommend you are buying DDR3L. It's a new and improved standard your model of MBP supports.