Hi there,
the A6 error code would usually indicate a problem being encountered when the BIOS is checking attached SCSI devices such as SSD's, Hard drives, DVD/CD writers, USB devices etc.
Have you checked the basic things, such as mouse & keyboard are OK?
Were there any noticeable issues with your Hard drives (slow performance, slower boot up times etc.,) before this problem started?
Are you using a USB Hub?
Have you added any new hardware prior to this happening?
Try removing all attached devices from the motherboard except mouse and keyboard, does this get past the A6 stop?
If it does then re-attach your devices one at a time and retest the system. If at any point the A6 error reoccurs then the last attached device is the probable cause.