Snakes keep dying

[snakesir]

Hello...
Sorry to just barge straight into the Help thread. But I need help. :P
Eh... I'm a 4-time ball python owner, all babies, all normal morph. All just gotten from the same pet store, treated the same, taken care of the same - plastic bin with paper towels as substrate (we're dirt poor, heh heh) and fed frozen-thawed prekilled pinky mice... WHEN they eat of course.
Thing is... they've all died. Inexplicably, with only one of them showing any sign of illness previously! I'm fearing I'm just a bad ball python owner, but I love the little things so much. I don't want to keep bringing them into the home only for them to die! T_T
Can you point out what I'm doing wrong?

I'll happily put up any info you need - including, with some difficulty, a photo of the newest snake "Caillou"...