As far as I can understand your post, your car is locked and you can only access the driver's door, and for that you have to use the mechanical key.
Is the remotely fob actually working?
Is the fob battery OK?
Is the locking system fuse OK?
Does the system need to be resynched/reprogrammed to the key?
You could do worse than to find a dedicated Vauxhall Astra forum online (should be really easy to find a few as the Astra is a typical boy racer / enthusiast /DIY-er car) and have a look for locking system problems. Maybe post there too.