first time using python to connect with sqlite3 getting error

I have installed Pyhton 3.5.1 version,

tried to connect sqlite to it with following code:

import sqlite3
conn = sqlite3.connect('test.db')

It worked well for first time so I left it as it was. Came back to computer and I tried to use the same code again

However I am receiving this message now all the sudden using the same code:

Traceback (most recent call last): File "", line 1, in sqlite3.OperationalError: unable to open database file

I find it very strange, because I haven't done anything special afterwards when using code for first time. I am new to Python and I have absolutley no idea why I get this. Any help would be more then welcome.