"The problem was with VirtualBox. It wants the 32 bit version of Mint and I had the 64 bit one. I would have thought it could handle 64 bits as win 7 and i5 processor are 64 bit."
VirtualBox can handle a 64 bit virtual machine, as long as it's the 64 bit version of VirtualBox. That is, your hardware, your operating system, and your VirtualBox installation all have to be 64 bit.