Your code is working fine on a 32bit Windows, if you want it to also run on a 64bit Windows, try this :
key = _winreg.OpenKey(
_winreg.HKEY_LOCAL_MACHINE,
"SOFTWARE\\Microsoft\\Cryptography",
0,
_winreg.KEY_READ | _winreg.KEY_WOW64_64KEY
)
result = _winreg.QueryValueEx(key, "MachineGuid")
print result
Reference : Change 64bit Registry from 32bit Python