Project hangs - peaks at full CPU when loaded

Hi - I am working on a project, not a huge one, very simple project. It was working fine till yesterday, today I just started it (I did not update anything in my machine, its all the same file, that I had saved yesterday night - when it was working perfectly). now the CPU meter goes to the red, and average keeps peaking. I am not even able to play back. Here are things I already tried

  1. Disabled CPI
  2. Ran LatencyMON
  3. changed the power options
  4. Removed all the inserts and plugins
  5. tried various configurations of my sample rate

What ever I do, it is not coming down.

HOW TO DEBUG THIS PROBLEM. How to find which VSTi or what is really creating this issue. This is so frustrating, I could not do any work today, was struggling, with this issue…may be time to move out of CUBASE.

SOS - Please help