AI've tryed different temps on the oven I don't open the oven either an it seems to go fine until nearly done an it sinks! So frustrating! Any ideas anyone please?

Is it a scratch recipe or a box mix?

AI've been using a box mix yes

You must be jostling the oven (by opening the door) before it is done. Give it another 5 minutes before checking and be extremely gentle, it won't collapse if it is baked through.

You MAY be putting too much batter in the pan.

I have a homemade recipe that does this from time to time....

OR it could be (as I have thought with my own recipe) that the batter that clings to the bowl after you fill your pans, which you scrape down and pour into the center of your panned batter MAY not have all the leavening agents equally distributed throughout, causing the last bit of batter to be virtually unleavened.  

So try scraping down your bowl and then running the mixer for another 15-30 seconds to get it all mixed well.

http://cakecentral.com/newsearch?search=rose+nails+in+baking&=Search

lots of threads here to research.  You may find several tips that help you.

I have a recipe that did this and it took me ages to figure out what I was doing wrong.  Turns out I was beating it for too long once the flour had been added to the creamed butter/sugar/egg mix.  Now I know that with this particular recipe I mix until just combined (even though the recipe says differently!) and it turns out perfectly each time now.

Hope that helps!

Cheers,

J   :)