I crashed my car, took it to a macanic and asked him to fix it. He got the car moving right but there is a grinding noise coming from somewhere. The guy did say to bring it back but prior to working on my car, a friend of mine had his hood fly off down the street after this macanic fitted it. Do I trust him and take car back or do I and can I file law suite and get a real macanic to do the job?

First off, it depends on what you had the mechanic work on, and if it's possible that the grinding noise is a result of said work.
Second off, you have to be able to prove that this is what took place, remember it's going to be your word against his, unless you had witnesses to the whole thing.
If you feel you have a valid case, I'd take it to a trusted mechanic, get their POV on the situation, have them do an estimate on the cost of fixing said problem before the previous mechanic had worked on it, and after.
Then if you feel that it's still something you want to pursue, you may find yourself saving a lot of other people money, but I think personally you are going to be fighting an uphill battle.
This isn't something that's easy to prove.

i crashed my car, took it to a macanic and asked him to fix it. he got the car moving right but there is a grinding noise comming from somewhere. the guy did say to bring it back but prior to working on my car, a friend of mine had his hood fly off down the street after this macanic fitted it. do i trust him and take car back or do i and can i file law suite and get a real macanic to do the job?

Like homebirthmom pointed out, there are a number of deciding factors for this situation:

1) What work did you have performed on the vehicle by the mechanic?
2) Do you have this work recorded in writing?
3) Can you prove that the mechanic did not properly repair your vehicle?

The grinding noise could be from a number of things; if you bent the frame in the accident, it could be causing a misalignment between any combination of parts on the vehicle. Frame damage has to be repaired by a body shop; most standard mechanics don't repair that.