There are no enemies to kill. I can't backtrack because I'm at the very beginning. If I go left the screen won't scroll ('cause I'm at the start) and if I go right I'm blocked by the stone. No enemies present themselves.
It sounds like what happens if you try to play the PAL version on NTSC or vice versa. If you are on a NTSC machine, make sure you run infeztationNTSC.crt.
That's exactly what it was, I had downloaded version 1.0 without realizing it was PAL. Grabbed the 1.1 and it works perfectly. Many thanks, great game!