Okay, this idea came at me out of the blue. It may have nothing to do with your situation, but... you know, just in case, I thought I'd mention it.
Yesterday, I was messing with some Alter Database statements on my personal PC, trying to move the files for the system dbs. Turns out that I can't start my services either now because I did the Alter wrong and it now can't find the Model DB.
Of course, this is my personal development instance, so it's no big deal to me to just re-install it since I obviously can't get in to properly change the paths to the system DBs. But, it's a thought for you about your problem. Did you use Alter Database to change the system DB paths? Did you subsequently remember to actually move the data & log files for the system DBs after you did that?
You can see in the Application log of the Event Viewer problems with starting SQL Server (if you haven't already checked there, that is).
Catadmin - MCDBA, MCSA
"No, no. Yes. No, I tried that. Yes, both ways. No, I don't know. No again. Are there any more questions?"
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