washing machine stuck on slow spin cycle?

hi,our washing machine is stuck is stuck on the start of it`s fastspin cycle,I think the problem could be the filter but the filter will only turn 1/4 of a turn then jam there could be something in it but i`m not sure.wehad a similar problem before then a sock was jammed in it when i`ve tried turn the filter this time it will turn easely then stop as if it has hit something solid like a button or a peice metal.any ideas on how to remove the filter