In many cases some antivirus also start HyperV with window start and does not allow HAXM to install. I faced this issue because of AVAST antivirus. So I uninstalled AVAST, then HAXM installed properly after restart. Then I re-installed AVAST.
So its just a check while installing as now even with AVAST installed back, HAXM works properly with virtual box and android emulators.