I know there have been many threads on this. I looked them up, but most were too specific to help.
I'll reprint the message just in case:
We apologize for the inconvenience, but Windows did not start successfully. A recent hardware or software change might have caused this. If your computer stopped responding, restarted unexpectedly, or was automatically shut down to protect your files and folders choose Last Known Good Configuration to revert to the most recent settings that worked. If a previous starup attempt was interrupted due to a power failure or because the Power or REset button was pressed, or if you aren't sure what caused the problem, choose Start Windows Normally. Safe Mode Safe Mode With Networking Safe Mode With Command Prompt Last Known Good Configuration (your most recent setting that worked) Start Windows Normally
I have tried them all, to no avail. Just before this happened a message box kept coming up, telling me that windows needed to update some software and restart. I kept clicking restart later until I left and came back to find it in its current state. So obviously the updated software is causing the problem.