(I have edited the post, with more information. It's my first post so sorry if I didn't explain the problem very well)
I have linux Mint 18.3 Cinnamon (64 bits). After the Miktex's last update (2.9.6615 version), when compiling my .tex (let's call it A.tex) file in Texmaker I don't get the updated PDF file. I made a new .tex file (B.tex for example) and then texmaker showed a window saying that the program doesn't find the .log file, without any error. I have tried to uninstall both miktex and texmaker and then install them again (firstly miktex and then texmaker), the problem remained.
Also I have installed Texlive, since a read a suggestion of one of you, and then texwork as editor. I tried again to compile the B.tex and it worked well, however, with my old A.tex it drops and error:
LaTeX Error: File `Classes/PhDThesisPSnPDF.cls' not found
It seems that the program doesn't find the place where the class of the A.tex is defined, but I don't know why. Before the last update of Miktex I hadn't had any problem and now I have it. That's why I guess it's because of the new version. I can't find the solution, hope there's somebody that could help me.
Thank you in advance!