Why did my conversion rate drop after switching to single page checkout?

[1985games]

Around May 15 I switched to single page check out and since then my reached check out to sessions converted has dropped by 50%. My traffic to the site is about the same but all my check out sessions are way down. I have tried reverting back to three page check out, I have tried disabling a number of apps, to no avail. All my days are down since then, none of my days are near "normal" sales.

Conversions went from 2% to 1% or less.