You may have accidently touched something in tile molester without realizing it. It's very sensitive and one wrong move will f the game up. My suggestion is when editing, always keep the icon with the magnifying glass clicked. If you have the icon that looks like a square clicked, and you click a certain area by mistake with it, it will screw up the entire rom. Even if you just TOUCH it without moving it or changing it, it will mess up the rom. So only click that box if you need to copy something from another rom. If you are importing a picture into the rom, place the picture where it needs to go, and use the magnifying glass icon. Click it once, and the picture will automatically import itself into the rom without any risk of damage. It's much safer than using the square icon. The splash screen, for example, is 32 x 28 I believe. So just make it 32 x 30, import the picture into the right area, and click the magnifying glass outside that area. The picture will import safely that way.
As for that rom, unfortunately it is no longer any good. You'll have to transfer your work to a fresh rom. I've had to do it many times lol. Like Smozoma said, use backups. I save tons of backups now after wasting so much time ruining roms by making stupid little mistakes. It's a waste of time haha. But that's how you learn. If you did any roster work, just use NOSE and copy/paste to a fresh rom to save some time.