Server load is ridiculously high – even without plugins

I’ve recently acquired a new server with i7 CPU and 12 GB ram. All went fine for a few weeks, crazy fast it was with 4 websites and around 15k visitors daily.

A week ago though, server load went to 10 / 35, even when only 1 wordpress site is enabled. All plugins disabled..

I hired two server managers to see what’s wrong with the server, server seems to do fine on fresh WP installs. As soon as I turn one of my ‘large’ sites back on, server load skyrockets up again.

I disabled all plugins, tried different themes, optimized & repaired all database tables, tried my sites 1 by 1 but as soon as I turn 1 on server goes berserk.

After 50+ hours of struggling with this problem, I’m pretty much desperate. I don’t know what to do next, i really really hope there’s someone here that has heard of the problem and knows a fix for this.

Thanks you very much

Chris