Windows 7 freezing during startup

[ombligos]

My technologically-illiterate father is using Virtual Box to run Windows 7 on his Mac powerbook. After updating to Yosemite, the wifi stopped working on the windows side. As a poor excuse for tech support, I used Chrome's Remote Desktop to access his machine and try to fix things. Switched the network preferences from Bridged to NAT and everything seemed fine.

Today, he cannot start windows at all anymore - although it worked after I'd changed his settings remotely. He has always gotten the dreaded black "Windows Error Recovery" screen at start up, but was able to just hit enter to select the already highlighted "Start Windows Normally" option. Now when he starts windows, the Error Recovery screen appears, but none of the options are highlighted and the keyboard ceases to function. So, he's just stuck with a frozen Windows Error Recovery screen and a non-responsive virtual box app (had to force quit).

Any ideas what might be going on here and how I might attempt to fix it for him?

Cheers!

[mpack]

Without details of the error it's impossible to comment on its cause.

See section 12.3.4 of the user manual: How to record bluescreen information from Windows guests.

Dare I ask if any backups exist of the VM folder?