[Plugin: WP Supercache] Stopped Caching and People Are Seeing Hompage from May

OK, I’ve had WP-Supercache working fine on my site artofmanliness.com for several months. But for some reason it just stopped chaching. On top of that, on some people’s computers, it has been displaying the homepage from May 9. I’m at my wits end with this. I’ve unistalled the plugin and reinstalled it; deleted the cache folder and still nothing. Nothing is absolutely chaching. I’ve looked at all the workarounds and tried them, but nothing. I’m using WP 2.51 and the plugin worked fine with it until just a few weeks ago. My site gets on social media sites quite often, so caching is really important

Any help would be great. I’ll even pay someone to fix it for me as long as they know what they’re doing.