some horses are just stoppers BUT some aren't, they are just green. So it depends on what you've got underneath you.
Firstly though, I would make sure that you didn't put him at ANYTHING that he couldn't clear from a standstill. Basically you have to teach him that stopping isn't a choice. So if he slams the breaks on, don't turn him away, keeping him facing the jump and make him jump it from a standstill - most horses can clear up to about 2' this way, some higher... so that should still give you plenty.
If he runs out the idea for you is to teach him that going AROUND the jump isn't a choice either. So pull him up quick (I mean quick - ideally before his nose gets past the wing). You will probably have to be pretty strong at this point. Then turn him back TOWARDS the jump - so if he runs out to the right turn him left back towards the jump) and then get him to face and go over the jump as quick as possible. dont' go 4 miles away from the fence before you turn round! It is mostly about determination and timing with stoppers. Many people are a bit passive with jumping, they allow the horse to go up to the fence at his own speed, then when he stops or runs out they sort of sit there for a couple of seconds going 'oh dear, now what do I do...' by which time it is too late to really achieve anything. ride assertively into the fence and when somthing goes wrong, deal with it immediately, even if it means being a bit tougher than usual. Keep the horse straight NO MATTER WHAT... Pull him up IMMEDIATELY after running out. INSIST he goes over the fence (remember we are only talking little cross poles here). Pretty soon he will realise that a) he has to do as you say and b) actually it isn't that scarey after all. He will also start to respect and trust you more to be the boss and look after him and be happier all round.
When he does stop, use your stick once, firmly behind your leg as well to make it clear that this is not acceptable. don't beat him/punish him or shout and get mad but one firm smack is often useful to reinforce what you are trying to achieve.
Ensure when he does clear the fence that you don't pull him in the mouth, thump down in the saddle, land in a heap etc so that he has a nice experience! (I'm sure you do this anyway)
Avoid approaching in canter for the first few times as it is much easier to stay in control of the horse in trot - be positive with your legs all the way in and give him a little tap with your stick about 2 strides away just to make it clear what you want. Carry a schooling whip rather than a jumping whip so you can keep both hands on the reins and keep him straight.
Some horses are just serial stoppers but some have just been allowed to get away with it and with firm positive riding will gain confidence and start jumping again. My pony when through a stopping stage but I cured it with Hunter Trials and very positive riding on my part - she never stops now and adores jumping... so it can be fixed.

They've put a man on the moon, but they still can't design a package for likits that you can open in less than 1/2hour