Check your system for updates.
Check your system for updates.
Explore all available repair and restore choices from the F8 menu. Windows update issues aren't uncommon—they often arise when the QA team was active, but now they seem more frequent. If everything in the main Windows tools fails, consider using an installation media with advanced utilities, such as a repair install.
It seems A2 is related to a boot problem with the storage drives. Remove all connected drives except the one used for booting. Also, reset the CMOS. This could also stem from a driver issue. Have you managed to revert your system using a restore point? Do you have any backups? If not, you can safely extract everything from the drive using a LiveCD or USB before proceeding with the installation.