Important Car Question! Need Advice. Need to Drive Up for a Cruise & My Car Wont Start! Please I Need Advice?

I noticed this week that the engine wasnt starting that great when I started my car, yet it still turned over. Tonight I went to go shopping and it barely started. I freaked out and noticed that my digital overhead car odometer said 0 miles till empty which is false because it should have had 113 miles left till empty. Boyfriend suggested it was siphoned and my friend thinks its a computer problem. I think I agree with her considering I did noticed it wasnt starting well. I originally thought it might be a battery problem but that shouldnt affect my digital odometer right? What do you think the problem is. Tomorrow Im getting road side assistance so I can get it towed to be fixed but I would like to know what majority of you think the problem is so I dont get blindsighted with a high price.

need more info to be more helpful.
what car? year? miles on it?
and also can you try to describe what is going before when having the problem, before when it was starting to give you issues and now when you try to start it?
does the cranking (sound of car trying to start) sound slower than normal? etc

so it starts up and makes noise while running at first?
or does it just make noise when you are turning the key/trying to start the car?

if it just has problems when trying to start it could be as simple as your battey cable clamps are loose, so just make sure they are tight. the sound of that would make a rapid clicking sound. the battery losing connection may cause the "miles to empty" thing (never seen one) to reset