TERRIFIC NEWB. FIRST GAME. NEED HELP ON CHIPSETS

I'm currently attempting to make a game full of 8-bit graphics. Currently, I'm a massive newb and in trying to make a ChipSet, I wouldn't be sure what the measurements for each different type of tile would be. So, instead of building one from scratch, I copied one of the RTP chipsets. Then, I take the graphic I want and replace one of the old graphics on the old chipset, reshaping the tile to ensure it's the correct size. However, when I try to use the chipset in the game, it appears as a black canvas completely. The new chips, the old chips left over from the RTP image, everything has been replaced by black.

It's in PNG format and it's the correct size. Is there something about my method of making the chipset upsetting it? Or am I missing something in general here?

Hrm. So this is no MSPaint job. XD

Thanks, I'll try that out.

EDIT: Huzzah! That definitely worked.
Thank you very much, trance2.