Yes, unfortunately there is an issue with latest updates to Grisoft AVG antivirus/security solutions on your MS Windows 7 64bit editions. Once you have manually or automatically updated the software your system becomes unresponsive and also once rebooted does not want to boot/start up your operating system.
If this is your case go to Grisoft AVG support forum and follow up troubleshooting steps as they are now available and it will apply work around and you will be able to boot up back to your Windows.
The fix is actually simple as you have to just boot up your system with some boot able media (Linux) or AVG Rescue CD disk. Onc eyou have booted up, navigate to C:WindowsSystem32Drivers and rename all files that starts with avg***(e.g. avgldx86.sys, avgtdix.sys, etc.). Also change their file extension from .sys to .bak. Once completed, reboot and you should be back in your system.
In case you cannot fix it by yourself, get in touch with Grisoft AVG support:
Home and Free customers: +1-877-367-9933
Business customers: +1-828-459-5436