Vauxhall Corsa car not starting check engine light flashing

hi my corsa isent starting and check engine light is flashing whene i turn ignition and whene i try start up car sounds like its going to start but doesent just turns over as if trying to start up. it started up ok couple of weeks ago thene ive done little work on it for its m.o.t just rear window wiper window and new strut dont think this will have enything to do with it there was a little oil leek comming from a sensor at front of engine just up from oil dip stick didnt fail m.o.t because of this but he said change it or ull lose engine oil could this be why not starting and why check engine light flashing? but it did start with this problem before and engine light wasent flashing before this if eny1 could help would be a great help thanks john