I have an NT4 workstation on a network with a dual boot option to DOS 6.21. I wanted to upgrade DOS to 6.22 so I did a 'SYS C:' from the a: drive. When I restarted PC I could not access NT. I reboted NT workstation setup disk and asked for a repair. I told it I did not have a repair disk & it told me it could not find NT operating system on HDD. I then attempted repair using repair disk. It seemed to work OK but when I reboted PC, it got half way through loading NT and then hangs. I can still boot to DOS.