How to prevent oracle database to start when windows boots up?

Go to Control Panel, Administrative Tools, then Services.

Look for a Service called OracleServiceXE. It should have "Automatic" Startup Type. Change it to Manual or Disabled by right-clicking it and then choosing Properties.

Works for me on Windows XP and 7. I don't have a Windows 8 machine, but it should be the same steps.

I think the solution provided here is useful:

https://dba.stackexchange.com/questions/62699/revised-question-how-do-i-prevent-oracle-12c-database-from-starting-on-machine

You have two solutions:

1- In Windows OS's in the run, type services.msc and Enter, from the list of services find OracleService and right click and choose Properties. In the General tab in the Startup, Type section choose Manual and click OK and exit. From now on your database doesn't start automatically by your machine's start, but whenever you want to start it you have to go to services.msc and start it manually. You can also do this from Windows Task Manager(from Services tab).

2- Let the Startup Type to be automatic in "services.msc". Open the Windows command prompt (Admin) and type this statement (instead of ORCL use your SID name).

oradim -edit -sid ORCL -startmode manual

Now your database is in a state that idiomatically called idle. You can start your database by logging to SQL*Plus with sysdba privilege and then type startup command.