Astra2.0cdx 2005model when blocking fuel supply it start even hot immediately connecting the supply it doesnt start ,ihave checked the timing it is fine but still wont start.

I would try a new fuel filter. Its possible that when the engine is hot, the fuel is vaporising causing the hard start?

Make sure battery has a full charge and battery connections all good.
If it cranks good but won't start, have a helper crank it while you check for spark at the spark plugs, if spark everywhere, use a gage and check proper fuel pressure. Also check fuel injector pulse. Any applicable trouble codes?
If the starter motor won't even crank the engine? Two voltage circuits to starter motor, one comes from the battery, hot all the time. The other circuit goes hot with key in the start position and is probably wired through neutral switch for auto tranny. The starter motor grounds through engine block.

start with the fuse panel . really look good. even replace fuses just in case. then look at the fire wall where it passes through the fire wall is there a connection block with a bolt in the center. . remove battery if you want to reseat it.
check the connections to the fuse box too. look for any inline fuses ,
see that all accessory ,lighter sockets are working , check the key switch in accessory position.
insert a signal into one of them end connector an trace it back with high freq . only a tech knows what an how to do this.

check fuel filter,air filter,tune up.

DTC P2047 Injector fuel supply rail pressure volume via volume control valve- rail pressure too low.
Poss causes1. fuel filter blocked (even Partially)
2.kinked or damaged fuel lines
3.worn fuel pressure pump
4.faulty pressure relief valve
5.blocked tank breathing circuit

since cap is new and rotor/ check engine timing and fuel supply for any block passages/ check battery and lastly if it doesnt start ur engine might have a loose compression and that needs full engine overhaul.

TAKE IT TO A MECHANIC !!!!!!!!!!!!!!

Check your acceerator linkage. The cablemay need replacing.

I don't know the model year? Key on engine off, use a gage and check proper fuel pressure. Then with key off, see if pressure holds for a bit? If it drops like a rock, check for a fuel pressure leak. If the engine is hot and trying to flood for some reason, your going to have a tough time. Any applicable trouble codes? Check your coolant temp sensor, only if testing leads in that direction.
Smell of your crankcase oil dipstick, does it smell like gas?

well there are a few things that can cause this and Im sure you have tried most but I will run down my normal list first fuel vapor lock is still a problem on high performance cars in the 80s try cycling the key 3 or 4 times from off to on pausing briefly between each cycle to push fuel through the lines if that does work check the location of the fuel line on the front of the block of it is touching there is your problem ok if that doesnt work coil saturation meaning the heat is actually causing it not to fire next would be the the distributor first cap and rotor wires breakdown plugs even do not use platinum or iridium plugs in anything that old even if you think its in great shape one speck of oil it wont fire through it then you have the electronic module in the distributor most chain parts stores can test them for you for free hell most are cheap for the older cars good luck and if you need clarification or more help let me know Danny