Stalled and will not start now

I was driving home on Saturday evening and started hearing a strange clicking noise when I reached sixty five mph. Slowed down a little and noise stopped. When I started moving back up to sixty mph I heard the noise again and felt a delay when I pressed down on the gas. Stopped at a red light and when I started moving everything locked up, including my steering wheel. It became really hard to turn off the highway. Then my car sort of rolled off to the side- felt like no gas to the engine anymore, and stalled completely. Everything else seemed to stay on (radio, lights, etc.) When my brother tried to start brakes were not functioning and when pressed on the gas it seemed to start for a mill second and go off. Brought car into the dealership and they said they do not know whats wrong and I could pay $800.00 to have them try new spark plugs and repair a valve, but that they are not sure if that will help, or I can pay $10,000 for a new engine and at that point it would be totaled and not worth it to fix. I paid $118.00 for a diagnostic with no explanation on anything and I am not sure what I should do. My truck has never had any problems before this except the emissions light has been on, but the dealership told me not to worry about that because it was likely a sensor issue because it did not come on for them. My SUV does have 150,000 miles on it, but the last mechanic who looked at it said it was in great condition and would likely last awhile. What could be the problem? I am not sure if I should invest in a new engine, have the dealership “try” the spark plugs and valve repair, or look into getting a new car. It just does not feel right to me because as I said before, I have never had any other problems and it drove fine on Saturday morning. No indication of any issues.
Dealership says its not the timing belt.