My Pioneer DVD 114 player will only play some dvd's. Why?
Sometimes wen disks are inserted it makes a clunking noise and nothing happens.
Please help as I can't understand why some disks work and some don't.

Hm. I have the same drive as you. Mine too has the clunking noise, but after some clunks it reads the disc. :D
Are all your discs from the same region, and is your drive region free? These drives are region locked from the factory. If you want to play discs from all regions, you need to flash it with a modified firmware, get it from www.firmware.fr.st