Windows Virtual PC does not support 64 bit guests.
Windows Virtual PC does not support 64 bit guests. See this chart. Note the complete absence of any 64-bit guest column. This hypervisor is emulation based, so you are stuck with whatever software they use to emulate the hardware/processor. If the emulator only emulates a 32 bit processor, you will only be able to use 32 bit OS and applications. Use another hypervisor that supports 64 bit guests, such as Oracle Virtual Box or VMware Player.