Gimp-2.9.6-std is not giving me any problems on win7. However, I have noticed that JPGs and TIFs of photos can take an inordinate amount of time to load compared to PNGs (or XCFs if I remember correctly).
Edit>Preferences>Folders>Plugins should list two directories, one in your own Gimp profile and one in the Gimp installation tree. Do you see them? Do they exist? Are there any file-something executables in either directory?
I am having this problem (GIMP gives an error of ‘unknown file type’ for JPEGS. I see you mentioned executables in the two Plugins directories. I have this. I installed the Resynthesizer plug-in in both paths (it wouldn’t come up from just being in the GIMP installation tree). After that, GIMP stopped being able to open/see .jpg files. Any tips?
Edit>Preferences>Folder>Plugins: you get a list of directories. In out-of-the-box Gimp, one is in your user files, and one is in the Gimp installation. The directory in the Gimp installation should contain many executables with names starting with file-: file-jpeg, file-png (file-jpeg.exe on Windows). If you only see the GMIC executables there, then find the directopry with the file- executables, and add it back to the list.