Cannot upload product images

[marcoz]

Hi, sorry to bother for such a simple thing but I guess there is something really wrong in my Prestashop installation.
Is there somebody willing to give me a hand ?
I upload images without any apparent error but they don't show in the SHOP. Also some very strange things happen.
I delete an image, try to upload a completely different image but the same old image keeps on showing in the backoffice only.
The front-office does not show any picture ....
Is not a matter of permissions, I already checked ...

Thanks a lot

P.S. is out there somebody wo could give a "professional" hand installing and configuring a PRESTASHOP ? Please contact me