1998 Vauxhall Astra starting probs

My Astra has this problem with starting, its takes ages on the starter before it catches, and when it does start the engine management light comes on and it loses power, you then have to wait until it goes out again to get the power back, apart from that it runs fine. i have had it fully serviced including the fuel filter, and put injector cleaner through it, so now i'm baffled, Help !!!!!!!!!!!