why wont my 04 plate clio start???

i have a problem, 3 days ago i drove 20 mins, popped inside for 10 mins, came back out, car wouldnt start, tried again 2 hours later started. drove 2 days later started dodgy but ignited. any way today it is pouring with rain, iv gone to start car, and it sort of coughs/splutters, inside the dash makes a groaning sound and thatts it?? all lights r working on dash, radio etc is, but my clock seems to of reset itself on the dash??? tried holding key button and turning just locks it, when i tried locking it it failed first time but locked when i pressed again, the light on the dashboard stays ON when starting up and flashes normally when off. im clue less as to wether its the battery, or immobilser?!!