Hi to everyone [:)]

I'm really excited to use this great software as my family is about to buy our an apartment. I created a file yesterday, but when opening it today I found that everything in the 3D view turned into red blocks, and the thumbnails of the furnitures, textures, ...etc are just a red cross. I made a few changes of the wall, added some textures and when I tried to save it got refused?

Anyone can help please?