Dont Know what it has

ok so my nexus 5 was fine until one day it just started to reboot by its self, its not the first time its happend, i have had the button replaced before too so this time i was gonig to do it again, sometimes i get it to turn on and it wokrs fine until i press it and the power off text pops up, i touch somwhere else so it gose away, and 1 o 2 things happen: it reboots as if i had kept holding it or it gose back to normal until i press the button again but the wierd thing is that when i connect it to charge(turnd off) it starts to show the google logo and reboots instead of the battery, and it keeps going like that until i disconnect it and when i do, it turns off, a friend had a similar problem with his s4 and y swithed the battery becaus he said the battery contacts were dirty and it fixed it but i dont think it is the case with mine