i found this mabe it could help
Ticket #12063 (new defect)
Using Windows 8.1 RTM and Virtualbox 4.2.16 with bridge networking component installed results in shutdown and
sleep problems
Using Windows 8.1 RTM single language (English, activated with serial provided with PC) and Virtualbox 4.2.16 with
bridge networking component installed results in shutdown and sleep problems. The display becomes dim and HDD spins
down (on notebook) but the power led is on and coolers continue to work. Changing drivers for network cards, video,
motherboard, etc doesn't help. Reinstalling Virtualbox with bridge networking switched off (NAT is on) helps to
completely resolve the issue. Devices used: HP envy 4 touchsmart, Acer iconia tab w700.
https://www.virtualbox.org/ticket/12063
James