Car won't start as it used to. It takes a few times before it starts.

This has been happening on and off for about 2 weeks ago with the snow, I had left the car off for about a week. This hadn't happened in cold days before. It used to start straight away even at 1 degree centigrade. Someone posted that this happens in cold days and that you do have to turn on and then wait for 20 seconds before turning on again. Do you need to keep button down for 20 seconds or leave for 20 seconds and start again?

Weather: 5 degrees centigrades. It took me 5 times before I could start it, first: radio on engine off, second: dashboard said Engine already on, third: no lights all dead, fourth: yellow ECU energy warning light stayed on, but then it disappeared once I finally got to start it properly. If this is a fault, would the 3 year warranty cover it? I have been using this car for the last 8 months, bought it nearly new.
Day before yesterday and other times: radio came on but engine didn't...had to try a couple of times before it started...Looking for suggestions, hopefully someone out there can help me.