How do I adjust the hood latch cable on a Mercedes 2000 E430.

You have not told me the year, make, model, or mileage of the vehicle you are driving, but here is a generic answer.
Since the early 1980's, cars & some trucks in the U.S. have had a hood release cable actuated from inside the car and attached to the hood latch.
(Bonnets are hats babies wear on their heads).
The wire inside the cable can break, or rust, or stick, as can the hood latch itself.
Hood latches are also somewhat adjustable.
You will need to have a mechanic open your hood from inside the fender, or from inside the bottom of the grille, so you can either replace the cable or lubricate it or the hood latch.
God bless your efforts.

Have someone press down on the hood with their palms while you try and release it, if it does open lube the hood latch with white lithium grease AKA "Lubriplate".

Quite often the hood latch will not release for one of two reasons. Firstly, the latch is gummed up with old grease, and secondly the cable is kinked and does not release the latch. I is also possible that the latch is damaged, possibly at one time the hood was forced down at a slight angle which could damage the latch.
First, check the cable. Unhook the cable from the latch by pressing the latch back as far as possible with a tool and unhooking the cable. Let an assistant pull the hood release inside the vehicle and feel if the cable moves in freely and you can easily pull it back by hand. If not, replace the cable. Do NOT close the hood while you have the cable out!
Next, check the latch for free movement. If ally is well the only other problem is the bullet hook on the hood itself which may be either loose or adjusted in too far,

have some one press down on the bonnet while you pull the cable knob as sometimes the adjustment makes it difficult to pull hard enough to undo the latch. If that works then adjust the latch before closing the bonnet

The hood cable is not adjustable, you must have a defective cable or the latch is sticking under the hood.

Sounds like the latch is slightly out of adjustment. Have someone pull up on the hood edge while you release the hood from inside. Once open, spray some white lithium grease on both components of the hood latch. The latch strike bolts usually have slotted holes to allow for adjustment. If you loosen them slightly, and then close the hood, it should align itself, then open the hood carefuly and retighten the bolts.. IF you cannot get the hood open, chances are the cable is loose from the release, and you may have to remove part of the grille to access the underside of the latch to replace the cable.

The cables and latch become dirty and corroded,and the spring wrapped cabbles can even rust on the inside.
The cable itself may have broke.
if you are able you can lay down under the front reach up through the grill and you just have to feel your way take a short screw driver and feel where the cable connects to the latch,use the screwdriver for a lever and pry the latch open.
once it is open have someone pull the release and watch for movement,if it does clean the latch ,spray cable lube into the cable while moving.
then adjust the latch a little,not to much at a time or the hood will be loose.
Of course if there is no movement in the cable it means its broke and will have to be replaced

can you reach the cable itself?,or is it broke at the hood latch?IF its not broken at the outside latch, try to follow the cable,un-hook it from the handle and pull on the wire cable to open it.IF its broken at the latch itself,you are going to have to reach the latch through the grille and try to pull the lever the cable connects to.That part is no fun at all..!!

THE HOOD IS MECHANICAL MEANING ITS JUST A WIRE PULLING A LATCH. HAVE SOMEONE PULL UP ON THE HOOD AS YOU PULL THE LEVER TO OPEN THE HOOD. IF THE BATTERY IS DEAD THEN GO TO THE REAR SEAT. ON BOTH SIDE RIGHT AND LEFT, JUST UNDERNEATH THE REAR SEATS ARE THESE LITTLE HOLES . FIT YOUR FINGERS IN THERE AND PRESS UP ON THE SEAT. DO THE SAME TO THE OTHER ISDE. THE BATTERY IS THERE UNDER ALL THAT STUFF. JUMP IT FROM THERE.

stretched or frozen... have helper bang on hood center front while you tug..once open lube abd grease all latch areas and cable end you see there...good luck