How to fix without reinstall.
Get out the credit card and be prepared to spend a few hundred with Microsoft. For the money they'll have you or will repair the OS for you. Most folk are not ready to pay for this.
There are also folk like Mark R. (link to follow) that repair the OS.
"Troubleshooting Boot & Startup Problems Learn how Windows boots, troubleshoot errors during logon, and fix unbootable systems"
You bring up a good point. That is, should Microsoft and all vendors have provided a tool to fix ALL windows failures without a reload? So far they have not.