Why my phone is not starting

@suraj71901 not a lot of information here. You really need to give us a more complete history of what is going on with your phone, and what you have checked. All we can offer at this time is a rather generic answer. Sometimes just a simple reset might work. So give this a try. Press the Volume Down and Power key until the Vivo X7 restarts.

Your phone is getting up there in age and I would start with the power requirements. First check your charger. Make sure it has proper output. Then check your charging cable. Check to make sure connectors are not bend etc. After that, check the charging port. Clean it of any debris etc, use a few puffs of air to clean it out. If none of this works, get a USB ammeter and see if your phone draws any amperage from the charger. If it does not it is possible that this is a charging port issue or a bad battery.

I suggest that you start with a new battery if any of the above did not work. After that you will have to check the charging port. In the case of your phone, it is soldered to the motherboard and thus requires soldering to repair it. To check it, use a voltmeter and measure the voltage on your battery connector. Next plug your phone charger in. Now measure the voltage on your battery connector. That voltage will have to have increased. IF not then the issue is either the port or the charging circuit. Your charging port is soldered to a charging board. You could replace that. Here is what the board looks like This is not an endorsement of the seller. It is only an example what you could replace.

Use something like this video to work on your Vivo.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!