1997 Sentra wont start, dead. Small relay buzz under hood, when turning on key. How m\uch voltage should be at the starter?

Battery voltage is 12.90 & Has worked perfectly up till 2 hours ago.

I just came across a car with the same problem, your starter is fine. what you need to do is first clean all your grounds, the one at the pcm, the neg batery cable on both ends and etc. if that doesnt work disconnect your neg. bat cable and the dissconnect the connect at the pcm and get a can of electrical cleaner and clean those connectors, and make sure to air them out before you connect them back to the pcm. then connect your neg. bat. cable back up and then see if the buzzing went away if it still is buzzing there are a few connectors i dont know exactly wich one but it would have corrsion in a connector that you would have to clean witht the elctrical cleaner and if that does not fix it you have to replace your whole harness from the pcm to all the connectors. cause right now with it the relay buzzing is causing your car to either not run or run like **** like its missing and will throw DTC check engine light on but to let you know ahead of time this is a seruois problem and if you dont feel comfortable with doing this i strongly recommend you to bring it to a nissan dealer cause you dont want to fry your pcm so be very careful.

Check your timing belt? does the engine turn over at all?