VW Golf 4 GTI, Oil pressure and vehicle wont start.

If your oil pressure light comes on
Don't ignore it. An oil pressure warning light (or low gauge reading) means one of two things: either your engine has dangerously low oil pressure (for a variety of reasons which we'll get to in a minute), or the oil pressure sending unit that triggers the warning light (or operates your gauge) has failed.
The question here is whether you have a serious problem or a minor one.
First, do not keep driving if the oil warning light is on or your oil pressure gauge has dropped. Stop the engine, let it sit for a few minutes, then check the oil level.
Is the level low? If the oil level is down more than two quarts or no oil is showing on the dipstick, adding oil to bring the level back up to the full mark may be all that's necessary to make the light go out. Just keep your fingers crossed that you haven't damaged the engine from running it too low on oil. If you hear rapping or knocking noises the engine starts, you're too late. The damage is done and now you're stuck with the consequences.
Note: On some late model vehicles, the warning light will come on (or a message will appear) if a sensor in the oil pan detects a low oil level. The light is supposed to come on before the level gets low enough to cause any damage.
If your oil level was low, it means your engine is either leaking oil or burning it. Leaks can be fixed by finding and replacing leaky gaskets and seals. Sometimes the oil filter will leak if it isn't installed or tightened properly. But an oil burning problem means the valve guides, rings and/or cylinders are worn or damaged and more costly repairs are needed.
If the dipstick shows a full oil level, then low oil obviously isn't your problem. The oil pressure may be low because of a worn or broken oil pump, a plugged oil pickup screen in the engine's crankcase, possibly a plugged oil filter or excessive bearing wear. Or, the oil pressure may be fine but the oil pressure sending unit has failed. Further diagnosis will be required to determine what's wrong.
Should you attempt to drive your vehicle home or to a service facility?
It's risky. If the problem came on suddenly, your engine does not have a lot of miles on it (less than 60,000) and you noticed no unusual noises (no valvetrain clattering or engine knocking), there's a good chance that all that's wrong is the sending unit. But, there's no way to know for sure without actually checking the engine's oil pressure with a gauge, or replacing the sending unit to see if a new unit makes the light go out. If the problem is only the sending unit, your engine still has oil pressure and you can continue to drive it until the sending unit can be replaced. But, if you're wrong you risk ruining your engine.
If you think you might have a low oil pressure or oil delivery problem because of a bad oil pump or one of the other problems we mentioned, do not drive your vehicle. Doing so only increases the probability of further engine damage. Have the vehicle towed to a service facility for repairs.

I had a similar prob on my Mk4 Golf GT TDi, it would only start when left for more than an hour - after the oil settled in the sump. Turns out the Golf has a safety feature that won't let you start the engine with low oil level. Topped the level up - hey presto! Sorted. Thanks 'mattvierra' your article was very helpful. Oh, by the way, don't over-fill the oil either - that's just as bad, you'll wreck the catalytic converter and they ain't cheap.

Hi my golf mk4 gti has run out of oil and now wont start after topping it up