open your door so thre isnt anything restricting your lock to work, push handle up into locking position then turn key,if turns ok and you can remove key then lock is ok and your door needs re-packing(toe and healing),i would'nt advise you to try and do this if you havnt had any experiance fitting upvc doors as you could end up with a door that wont lock at all,call a upvc repair company in your area and get them to do if asap as you will damage lock if you keep forcing it shut.hope this helps
shaun www.sdwupvcrepair.co.uk, June 2008