if you have replaced the head gasket and timing is correct. and u say the starter selonoid "fires" but wont turn over,
IT IS most probably a faulty starter motor, all corsa "B" built b4 1996 have the same problem of not starting, in the case of my last two cars, 1995 and 1993, they stopped working in middle of summer. the pin that engages the starter gear jams up. give it a tap with a long metal rod on the back end, (look straight down the righthand edge of the intake manifold). it it starts, then head for breakers yard n get new starter, about £25, and 3 bolts
J3DD, February 2010