Unexplainable non start

Just bought a 98 Cabriolet. 4 cyl not GLS. 72000 miles. Single owner. Has run good for two days. Daughter was driving and heard some rattles at slow spped. Turned it off. Now it doesn't crank. By this, I mean the electrics work, the dashboard lights up but absolutely no cranking when I turn the key. Will not turn over, makes no noise of any kind. Battery seems okay and I tried jumping the car off but the same thing. It did have check engine light on when I purchased it but ran okay home and the next day there was no check engine light. My mechanic said if the light wasn't on, he couldn't get a fault code. I am absolutely scratching my head. Is there some type of master fuse or switch that is keeping this car from cranking? I checked all the fuses belwo the steering wheel. All okay. There is some type of fuse below the spherical coolant container under the hood. I don't know its function.

Help!

ignition switches are a common failure on theese. Try wiggling the key alot while trying to start it.