wk2 – missing/corrupt ntoskrnl.exe file

So last night my machinge re-booted on it’s own. When it restarted I received the message “ntoskrnl.exe file is missing or corrupt, please re-install copy” I would appreciate any ideas how this can be accomplished as I cannot start the machine.
On a second thought, I am guessing my H/D has failed as on machine boot it is not recognized. My configuration is two H/D’s. The primary has(had) the O/S and the slave has the applications and data installed. If it is the case that my primary drive has failed and once I purchase a new drive, what are my options for installing the O/S and keeping the data on the slave drive. I do realize I may need to re-install the applications.

Thanks