Start with the latch mechanism under the hood. If it is sticking it won't catch. Unlikely to be the cable release. You can use WD40 to loosen it up, but that isn't a lubricant so once you get it moving use a white lithium grease.

Check that the cable moves freely by having someone operate it inside while you watch it under the hood. There is no latch inside the vehicle, just a cable and pull handle.

If you have had a bump,or some bodywork done, the height of the hood may need to be adjusted. The adjustments change the height of the hood and the length of the striker pin. If the hood is too high the latch can't catch. Unlikely to need adjustment unless something else changed recently, ie collision damage.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue