2000 Vauxhall Astra light staying on

this is known in the trade as a dearler engine management light and only some diag testers will read it. take it to a well known garage and they maybe able to help i have heard that halford/nationwide autocentres have had some new gear for this kind of thing and have helped me out loads with mates problems!!!!!!! if you have to pay its about £50 and they will find the problem and if not you dont have to pay!!!

get a daignostic done to check fault codes

The light you describe is not the engine management light this light means you have an electrical fault if it shows a yellow engine then this is engine management.You realy need to get the vehicle scanned for fault codes as you say the vehicle is slow at getting up speed then this would indicate a fault somewhere in the engine control side of things which should light up the engine management light but doesnt always as i took one in for repair today with the same problems but its not giving me any fault codes so im going to have to go through the whole system manually tomorrow.Once i find the fault i will give you an update to see if it could be the same problem that you have hopefully its not what im suspecting but they are prone for ecu failure which im thinking due to the power loss along with the electrical issue then it could be.Ill get back to you as soon as..