I can not figure out what exact part is broken

Hi i would like to ask if you cold advise me what might be broken in my iphone. My iphone 4s feel down from like 30cm and shut down. After a while it started up again and everything was fine. But after a while it shut down again for no reason. and then i was not able to star it up unless i connected it to charger. Now my wifi button is missing (black spot instead), everytime i start up iphone it says its 1st of January and its 1:00 AM, it also show my battery is full and i can not connect to my phone operator to call. I noticed a small gap on top, between back and case of the iphone (its really tight but you can put paper in it). Thank you for every advice. PS: I know its not easy to tell what might be broken but i want to epair it by myself and i don know what part of the phone is broken. The i will find a guid and repair it. Thanks for advice.