kieran sti 2

Hi my Impreza has trouble starting when slightly warm. It's fine when cold, and hot, but if it's anywhere in between it wont start. If I go on a little trip to the corner shop ( less than a mile away ) when I try to start the car again it won't, same thing happens when I've been on a long journey and Then let the car sit for 20 mins.
A little light comes on dash like a box with squiggles in, think it's oil temp light, it lights up as the engines turning over.
Any ideas wat could be causing this? Cheers