Win 10 unable to boot after AVG update

AVG Protection
3

Hello Philip,
I do understand your concern. I am sorry to hear this. May I know which AVG product you have installed ? May I know how did you updated your product? Please do contact us back for further information.
Thank you.

1

This morning I was notified that an AVG update had been downloaded and I needed to reboot my system.  So I did.  Immediately on starting, I received the message: Your PC/Device needs to be repaired.  The operating system was not loaded becaue the digital signature of a file could not be verified.  Windows\System32\Drivers\avgmfx64.sys  Error code: 0xc0000428"

As I am still running version 10074 of the pre-release version of Win10, I have no 'source disks' that I can use as a repair.  My system - which has vital information that I need to access - is totally unuseable.

Please advise as soon as possible what can be done to restore my system - and why an AVG update trashed it in the first place!

2
Hello Philip,
I do understand your concern. I am sorry to hear this. May I know which AVG product you have installed ? May I know how did you updated your product? Please do contact us back for further information.
Thank you.