Sounds like a corrupt effect, source file or project. Enable CapsLock and then hold down Shift when you click the project file to start AE, which should close all the comp windows. Another way is to split the project into halves to try to find what comp or layer is causing the problem.
I have tried that... unlikely it's a corrupt source/project problem I would think as I can swap across to the laptop and it opens no problem... possible it is an effect problem I guess... although I just tried making fresh projects with same effects and still no good.... I have removed almost everything in the project and saved a copy... no good... I have reinstalled AE twice... no good
I even tried saving it out CS5.5 and opening in CS6... still locked up..... so frustrating
Check your system's CoDecs/ Quicktime. Something has changed there, possibly, and now soem setting is incompatible with AE's stored data. Likewise, manualyl flush any AE relarted caches to avoid issues with corrupted cache data being associated with your project.
Sounds like a corrupt plugin if you get the same problem if you apply the same effects to a new project.