My server crashed and I can't figure out what the hell happened.

The specs:

2K Server
1.9ghz AMD
768MB PC2300 RDRAM
DVD Drive
DVD Burner
Onboard sound
Promise PCI IDE Controller

I had a external usb 2.0 250gb maxor one touch backup drive connected for several days prior to crash.

I was copying data back and forth between my HD0 and the usb external drive remotely through vpn. All of a sudden, I get disconnected from the server but I'm still on vpn. I can't ping the server or anything. I disconnect and decide to wait to figure out what is wrong once I get home.

I get home and I'm greeted with:

No operating system found:

I boot to my trusty HIRENS cd and use several diagnostics tools to figure out what happened.

NTFS DOS can't read HD0 but it can read HD1, HD2, HD3
None of the partition managers show it as a valid NTFS partition. But it can see all the other HDs and their correct states.

I run some maxtor harddisk diagnostics tools and everything passes.

I've come to the conclusion that the partition got corrupt and the HD is still good.
Afterall... the HD is less than 6months old.

I didn't loose any data. I have everything backed up.

I should be able to just format/reload.

But I won't... until I figure out WHY it happened.