It may be due to your OS not being compatible with QVM. Please check the below list for OS compatible with QVM.
|OS list for QVM support*|
Server 2003 R2
Server 2008 R2
Server 2012 R2
|Red Hat Enterprise Linux||6.4|
|Suse Linux Enterprise Server||11|
*If you do not find your VM OS listed above, you may not be able to use this VM using QVM or you may not have audio support due to the lack of support for proprietary drivers.
If your QVM does not fit the output monitor, please refer to this link.