Sandbox startup stalls in Windows 7

I installed Oracle VirtualBox software (for Windows) in my laptop which runs Windows 7.

Laptop memory is 4 GB RAM. It is 64-bit Operating System.
I could import the Sandbox 2.2 file (appliance).
VM got created properly and I clicked on START.

The start process stalls right after the step “Starting Knox Gateway”

I stopped several other processes (MS Outlook, Lync and others).

Not only it stalls at this point, the whole system almost freezes.
I had to do brute shutdown (removing laptop battery in order to force shutdown).

So far, this has happened twice,

Any advice?

Thanks