Whenever I try to login into SQL*Plus (11g Standar Edition Win 64) I get an error related to some connection error.
I try to login as sys as sysdba and provide the password.
All the services are started. I'm on Windows 7.
Any help would be appreciated.
The answer is
The major issue might be the oracle database itself may not have started. So, you need to manually go via
run command -> services.msc
check for OracleXEService surely, it may be disabled
right click go to properties-> set it to Automatic and press Ok. Then just right click again and start.
This will start your database making you to connect to it
Finally, In sqlplus command line,
connect as sysdba
enter username as admin
then press enter, you'll be connected
Ensure the OracleService is running. I keep running into this error, but when I go into Services, find OracleServiceXE and manually start it, the problem is resolved. I have it set to start automatically, but sometimes it just seems to stop on its own; at least, I can't find anything I am doing to stop it.
Use this command, in command prompt
sqlplus userName/password@host/serviceName
Go to Start --> Run--> type " services.msc"
Select the OracleService name, Right Click, Start.
Wait for a while and then your service will start. Then go to your sql command line window and try to connect to your user. I hope you can do that now.
Make sure your oracle services are running automatically.
Just press Win+R. Type services.msc in textbox then press O to find oracle services. 
In your PC name might be like OracleserviceXYZ.
Right click on highlighted services.
Another possibility (esp. with multiple Oracle homes)
set ORACLE_SID=$SID
sqlplus /nolog
conn / as sysdba;
You are getting ORA-12560: TNS:protocol adaptor error becuase you didn't start the Oracle database.
You can start Oracle database like this.
From START-> select Oracle Database 11g Express Edition( 11g or what ever your database type.you can find this from All Programs).
Then inside this folder there is a DB icon with green color spot.
It is the Start Service icon.Click it.Then it will take some seconds and start the service.
After getting the above message,again try to connect through the SQL plus command line by giving user name and password.
Try typing all of this on the command line:
sqlplus / as sysdba
As what you are doing is starting sqlplus and then using sys as sysdba as the user-name which is incorrect as that is not a valid user. By using the above command Oracle is using your system login credentials to access the db.
Also, I would confirm that the sqlplus executable you are running is the correct one by checking your path - ensure it is in the bin of the server installation directories.
Enter SQL*Plus with:
sqlplus /nolog
And then:
connect sys@<SID> AS sysdba
Try
sqlplus sys/<your password>@<your SID> as sysdba
You might have set oracle not to start automatically. Goto Start and search for Services. Scroll down and look for OracleServiceORCL (or OracleServiceSID). Double click and change startup type to automatic if it is set as manual.
Source: Stackoverflow.com