Very simple to solve this problem.
Just open RUN window(Window+R) and type services.msc:
Services.msc window
Find the SQL within name column and right click on that.
right click on SQL as in screenshot
You will get properties option, click on properties.
One new window will be open and there you have to click on Log On tab. And select the Local System Account. then apply and okay.
Select Local system Account
After that come again in services.msc window. and right click on sql and click start.
And finally, SQL Server services started successfully. enjoy and keep learning.