I am a new user of  Sublime text. 
It has been working fine for a few days until it began to refuse to compile anything and I don't know where the problem is. I wrote python programs and pressed cmd+b and nothing happened. When I try to launch repl for this file - that also doesn't work. I haven't installed any plugins and before this issue all has been working well.
Any suggestions on how to identify/fix the problem are greatly appreciated
Yes, you might want to give more detail. Have you made sure you have saved the file as .py? Try something simple like Print "Hello" and then see if this works.
Build command in sublime text has stopped functioning