Geeetech

I am tryng to compile Marlin, and am getting a strange thing happening.
Arduino 1.8.0, Windows 10 (yuck). Geeetech G2S (pro).
When I compile, I am getting a message that says "Marlin.ino already exists"
Looking atthe IDE, I see two tabs entitles "Marlin". They are different from each other. The second one has a strange little S-like symbol that looks like a pregnant S.
When I make changes in SDBaseFile.h and SDBaseFile.cpp (changing fpos_t to fpos_i3t), when I compile, save, and quit, next time I load Marlin.ino, my changes are gone.

Very weird. Any ideas?

Never mind. I found the problem, though I am not at all sure why it did what it did.
Turns out I have a Marlin.ino as well as a Marlin.pde
Compiles fine now, and I can finally get back to talking to my printer.I've had it for about a yrear now, and have not found the time to get it calibrated and in use.