Your system may be hiding "well known extensions" so all that you see is a file called "mod" instead of "mod.ini"
To fix this:
In Windows Explorer (My Computer, same thing), hold down the Alt key on your keyboard, and then press the T key and release both. Now click "Folder Options..." or press the O (not zero) key on your keyboard. Click the "View" tab.
Now, you should see some settings. Of interest are:
"Hidden files and folders" -- you can set this to "Show hidden files, folders, and drives" and it will show you stuff marked as "hidden" (note that it may be marked hidden for a reason (like it's important!) so be careful.
"Hide extensions for known file types" -- this is the one I'm referring to above. It masks the .ini or .exe or .whatever extension, unchecking this shows it (and allows you to change the extension by simply renaming the file -- note that this can be very useful (if a file has the wrong extension, say) but also can make files not work correctly, e.g., if you renamed mod.ini to mod.exe, the file will attempt to execute as a program and will fail, and you won't be able to open it in Notepad (unless you opened notepad and specifically told it to open mod.exe). This is easy to fix, simply rename mod.exe back to mod.ini and everything will work correctly again.
"Hide protected operating system files" (Recommended) -- this one allows you to un-hide protected OS files. Useful if you know how to get out of a mess and want to change something in your system; leave it alone unless you know what you are doing (if you don't know the significance of the F8 key while booting and using System Restore from the "Repair your Computer" boot option, definitally don't mess with it!)