dwf 410 ss smeg slim line dishwasher doesnt wash dishes?

the dishwasher, no matter which cycle, will beep as normal take in water and then will hum, for the duration of the cycle, the door will release for the tablet and then it will drain at the end of the cycle. but it would appear the spin arm at the bottom doesnt spin, and it was heard knocking as it was spinning the last time it worker, there were a few times where it didnt was properly, so i redid the cycle and it worker fine, i have tried it after it has been switched off for seveal days and have cleaned the holes on the arms,

any help would be greatly recieved.x

thanks

Shin
January 2010