From what you have described I would check the timing as soon as possible, don't run the engine if you can avoid it. The timing arrangement on these engines isn't perfect, in that the rear exhaust cam doesn't have a large contact patch with the cambelt. As a result, cambelt slippages are a known issue on 24V 164 engines - Alfa revised the timing arrangement for future V6 models. The belt and tensioner need to be changed within the service schedule (if not sooner) and if this has not happened then be wary! These are of course interference engines so if the belt has slipped valve and/or piston damage is a distinct possibility.
If it's not the timing then it could be a vacuum leak, caused by a split in the large rubber intake hose between the plenum and the MAF, or by a split in any of the 6 rubber seals on the chrome intake runners. You could also have any of the following:
A faulty MAF
A faulty air idle valve on the back of the plenum (recently changed this on my Q4, improved the engine's responsiveness - old one was all gunked up!)
Faulty coil pack(s)
Faulty fuel pump and/or splits in the rubber hose in the petrol tank (a common problem as these cars age; typified by taking longer to start and cutting out)
A faulty crank sensor (though the car probably wouldn't fire at all if this were the case)
And so on! I hope this post was of some use to you... it's probably best to start by checking the timing. To do this properly you'll need access to all 4 camshafts, which means removing the intake plenum and both cam covers. Rotate the engine to TDC (should be a small notch on the crank pulley that lines up with a small triangular marker on the block) and check the timing marks on all 4 camshafts (these marks are on the end of each camshaft, and should line up with the metal casting that surrounds them). This should all make sense when you have a look.
Try jumping the pins 87 and 30 with a piece of wire. You'll need to remove the relay to do this. This should show whether there's an issue with the fuel pump and realistically I would expect the car to run if you do this.
Did you check the timing? As that is a priority above anything else.
I had no-start situations on a few occasions before, even when engine was hot and had been running normally before stopping and restarting. Twice were in the parking lot; the first time I drove it within the car park and stopped somewhere for a quick wash,but car refused to start afterwards; the second time I drove it to work and after work it refused to start. It did not happen regularly, but randomly, and on the first two occasions, cranking the engine like hell solved it. The third time, the car was dead for a few days until I took an Alfa specialist to rescue. Before he arrived I told him the symptoms and he quickly felt that it must be fuel lines, stressing that Alfa 24V engine is the easiest to start. It turned out that the little rubber tube that connects the fuel line from the back to the fuel regulator in the engine bay (see circled part in picture) had aged so the capillary action failed and the engine received no fuel. Injected some WD40 (actual fuel better but had no device to suck from fuel tank) into the rubber tube sorted it. Engine fired right up. Wonder if your car has the same problem. Otherwise it could be the fuel pump, fuel regulator, or a vacuum leak in the fuel lines.
Thanks for The reply, i found The problem, it was the red stripe relay that went south haha. Replaced the old relay with a 87a relay but it couldnt fire the engine up so Got a double 87 relay and started first time!