2005 Vauxhall Astra Car not starting

You need to check the fuel pressure and check to see if it is getting a spark from the ignition coils.

The easiest thing to do is to remove the air snorkel from the intake manifold and spray some car cleaner into the throttle (throttle open). Replace the air snorkel and try to start the engine. If it now starts, or attempts to, the problem is fuel related. Check fuel pressure.

You'll need a fuel pressure gauge to check the fuel pressure (sometimes you can rent them from a local auto parts store). You can get fuel pressure specifications from a repair manual (at the auto parts store, or online).

To check for a spark:
If you engine has the coil-on-plug ignition system, remove an ignition coil.
With is still connected to its electrical harness insert a spark plug into its boot. Be sure that the spark plug is touching a metal part of the engine.
Have an assistance to spin the engine over while you observe the spark plug to see if there is a spark.
If so, the problem is not with the ignition system.
If not, let me know and I'll assist further.

The job of the battery is pretty straight forward during the starting process. It supplies power to make the engine spin over (crank). I don’t think that the battery is the problem. However, have the battery charged at a local auto parts store. Some will charge it for free so call around to see if the stores in your area will.

If you are able to get the engine to spin over, even by using jumper cables, then that part of the equation is taken care of.

The fact that once it does spin over, it still doesn't start is the problem we need to figure out.
An engine needs compression, fuel and, at the proper time, a spark at the spark plug wires in order to start.

Since you can get it to spin over, I suggest checking fuel pressure first since its easier (your engine has a Schrader valve (looks like the one on a tire where you put air in), where you can connect a fuel pressure gauge to check fuel pressure (fuel pressure is important since pressure is needed to make the fuel spray from the fuel injectors into the engine).

In case you don’t have a fuel gauge (or can’t rent one) you can circumvent the entire fuel system by removing the large air tube that runs from the air filter to the intake manifold (called the air snorkel), spray carburetor/throttle cleaner into the intake manifold. Re-install the snorkel and then try to start the engine.
If now it starts (and runs for a couple seconds), or at least attempts to start; then you know that the problem is fuel related and more testing of the fuel system is needed.
If it doesn't try to start, we must test the ignition system and check for compression as well.

Let me know how it goes, or if you need help testing the ignition system or checking engine compression.