Hello, 

I have a small manual lawn mower (Husqvarna) and now the wheels are blocked to move forward and the blades do not turn, but the wheels roll well backwards I think the problem comes from inside the wheels but there are no bolts to disassemble Do I have to disassemble the whole mower, including the blades, to remove the wheels and then, what is the problem; lack of grease, dirt etc? have you ever had this problem? thank you

A quick look at Google, if it is the same model, they is a small disc in the middle of the wheel ,I would say if you put in a small screwdriver that should leaver off ,giving you access to the nut on the wheel ,which should come off giving you access to the blade drive ,as you said probably dirt in they ,and some grease would not come a miss.

You could look up your model on YouTube could well be a video on how to take it apart and clean it all up.