This is the link to Play Store: https://drive.google.com/open?id=0BwG_Yelkqn0XYmk3cV9Xel9pdlE&authuser=0
To check whether you have got enough system storage or not, please watch this video http://youtu.be/qLpYnVDYDwM?list=PL6oDA8S3RmtGFmbUziIYK6j2aVRKp3B3k.
If you don't have enough space use link2sd to free up space. Watch this http://youtu.be/v7-toPSPFdg?list=PL6oDA8S3RmtGFmbUziIYK6j2aVRKp3B3k.
Use this method only when you have sufficient space on your System storage but Google play store still come up the error. Otherwise you have to transfer the applications (ones that are allowed) to the SD card or Phone USB.
The older google play store had a defect that lead to battery drainage. Then also you have to do as the video suggests. Thanks for watching.
How to deselect the Unknown Sources click here http://youtu.be/xEUnYSrU2Ns
Guys if your Google play store is not opening go to settings,then application manager , then go to all, next go to downloads,and finally enable it,then it should work.
If you watch carefully you'll see that I haven't uninstall the play store but rather uninstall all the updates. Hence, you can always reinstall the updates and can go back where you have started. Best of luck!