Any ideas why my Boot wont open?

The tailgate on my Megane Estate 2005 won't open took the switch out and cleaned it and sprayed it with WD40 replaced it and it worked a couple of times then didn't work again.
Repeated above process and got same results.
Went to a local scrapyard and got a replacement switch fitted it but boot still won't open
Any ideas greatfully received.
Thanks in advance, Graham