Not to say there aren’t a few thousand other people running Domino on a windows system with that many users – I’m not such a glutton for punishment. I would strongly suggest you convert over to a Linux system to push Domino. Yes, I know Windows is all “user friendly” and whatnot, but Linux is stable and that’s what you need. Not meaning to sound rude or anything, just some friendly advice.
As to your actual issue: Right Click “My Computer” on your desktop, then navigate to Properties -> Advanced -> Startup and Recovery. Make sure you have “Write an event to the system log” checked and “Automatically Reboot” unchecked. When your system BSOD’s, write down the error message and post back with that.
This is NOT going to fix your issue, but it will give you (and us) something to look at other than a constantly rebooting machine – which can be caused by a myriad of things.