Well, I'm not an expert on mobiles (mine's a Nokia model 1616), but you could try this: I think the screen display shuts down just to save the battery, but the phone is probably still 'live'.
To store a number in the memory:
1. Switch on. 2. Start display appears. 3. Display changes to show 'loud' or maybe 'soft'. 4. Press white bar above green symbol on call key. 5 Symbols display appears. 6. Scroll right to to phone book symbol. 7. Press white bar above green symbol. 8. Scroll down to Add Contact. 9. Press white bar above green symbol. 10. Enter contact name (not number). 11.Press white bar to enter contact name. 12. Enter phone number. 13. Press white bar to enter number. 14. Faces display appears. 15. Use scroll key to select a face. 16. Press white bar to ente. 17. Confirmation of name, number and face appears.