car shutting down and will not start.
Does check engine light turn on? If so, ask shop to read the diagnostic codes for you, then post them here for some ideas. If no warning light, and car won’t start, first step is for shop to determine if problem is no fuel or no spark. In most cases it will be one or the other. Something you can do yourself, make sure you have gasoline in tank.
I vote alternator. If I can have a second guess - Out of fuel. Let us know if it was that.
A bad crankshaft position sensor can cause a car to shut down and not restart.
One more possibility - bad battery. Have you had it tested?