Share your experience!
Do you get a error notification?
settings > apps > all > play store > clear data > unisntall updates > restart the phone
Does it work while on safe mode?
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008#U348008
Then its a third party creating this issue, either an antivirus, taskiller, battery app, data monitor, etc.
But you just proved it that it works while on safe mode, but it doesn't while on normal mode, that indicate a third party acting up.
Unintall any taskiller, antivirus, ram apps, battery apps, booster apps, clean master apps, etc. Also, have you disable any other app or service or background data on the playstore?