Nobody can tell you anything without proper system info or other technical details. The current time indicator behaving erratic can have all sorts of causes and judging from your info panel's "not realtime" comment you simply have a configuration problem with your graphics or audio.
I have 4 GB RAM , Windows 10 home , and AMD R7 M360 2 GB graphic card. So
what shall I do now?
just stating the obvious but the CTI behaves in the following manner: when you move it manually - it is blue, and when you playback - it's Red. if you have a playback issue you should check you Preview settings maybe you should reset your preferences.
in terms of RAM in seems that you are scraping the bottom of the system requirements for CC2015. RAM has a direct impact on Preview so problems with Preview could relate to that.
other then that you need to provide the full number of your Ae so we can see if that's the latest of it's release. there were a few bugs at the first release of CC2015 and some of them are preview related. you should consider upgrading to the (if you haven't already) new release - 13.8 is better in terms of Preview in my system (Windows 7). and if you can - get more RAM.