Hi guys I have an issue with my MBP mid 2010 15 inch

My MacBook Pro mid 2010 it’s screen suddenly shuts down and he restarts I thought that would be the macOS I removed it and installed the latest supported macOS and it still restarts then I thought of the rams I changed the ram modules and still it restarts by itself but when I am at the login page it doesn’t restart and when I login and lunch safari or Google Chrome it restarts