Malware will often detect the presence of a VM and refuse to run, requiring you to identify and defeat the VM checks or more insidiously appear to run normally but modify the actions it takes. [0]

Generally these problems are solved by modifying the VM so it can no longer be detected. [1]

[0] http://malware.dontneedcoffee.com/2016/04/bedepantiVM.html

[1] http://www.kernelmode.info/forum/viewtopic.php?f=11&t=3478