Sliding doors cant open

I tried to unlock the sliding doors which have not been opened in a few months. There seems to be no way to unlock it with the key, ,it usually open no problem .the key turns a little but no click which usually means door is open. I want to avoid a lock smith any ideas on what can be the problem thanks, tried WD 40, tried putting pressure on door different ways to see if it might work, anyone know a lock smith in dublin 12 area which is fair on price

Have they "slipped" up or down on the tracks while they have been sitting unopened?
If this is the case, try lightly pushing the door upwards and then downwards while trying the lock.

try pushing the door towards the locked side and then try the key while pushing sometimes this works,if not then you need to contact your local window company or ask someone you know in the window trade.