I tried to start my 2007 Ford KA this morning but it makes a very high pitched screeching sound. Almost like a grinding.
The car won't start at all.
Could you please advise on what this could be?
This is usually the telltale sign of a weak battery. The grinding sound is typical when the starter motor isn't provided enough power to turn the engine over.
Have the battery tested to confirm that it is weak prior to replacing it.
Sounds like it could be a worn pinion on the starter motor or worn teeth on the ring gear on the fly wheel. If you feel confident, you could - turn the ignition off, put the car in 4th gear (this will only work for a manual car), take your foot off the clutch and take the handbrake off, then try to nudge the car a little to get a different set of teeth on the flywheel exposed to the starter. Put the handbrake back on, take it out of gear and try to restart. If it now starts, then you need to get the starter/flywheel ring gear checked/fixed.
Best try this with someone else to give the car a nudge while you are in the car ready to press the foot brake if needed. Don't try this if the car could roll away on a slope. And only try it if you fully understand what you are trying to do.
It could also be just a low battery as Zaid suggests.
Well when you start most cars, you close a circuit that magnetically pushes the starter gear to come in contact with the engine and rotate it. After the engine successfully starts the starter moves back to it's position. Since you describe the sound to be similar to "grinding", this could either mean that the starter gear is worn out (the starter moves properly but the gear is worn out and can't rotate the engine) or the starter is stuck and won't move into position at all, or touches the engine just enough to produce the "grinding sound". The latter (which is more likely) could be due to weak magnetic field (maybe cause of a weak battery, or an electrical fault) or due to a mechanical failure that prevents the proper movement of the starters head.
You can't really do many things without taking out and examining your starter but try these. First try to start the car, by rapidly and firmly turning the key. pause for at least 10 seconds in between. Don't insist if it won't work instantly and don't try it more than 2-3 times. Add a battery booster or assist the starter with a little extra charge from your friend's car. Again don't insist more than 2-3 times.