Php server problems

Hi,

ive been struggling for a little while now with a feedabck form in my flash site that uses a php file to send an email to me when someone leaves feedback. I know the coding is fine because when i try it on a different host server it works fine. However, it isnt working on with its actual host server. I just dont recieve any emails. Ive been in touch with the hosting company but it is like getting blood out of a stone. It worked originally but very briefly. They say when they change the email addressin the recipient string and test it it works fine…but ive changed it loads of times to different addresses and tested it and nothing happens. Any have any ideas what the problem might be…i am not very techno savvy but would be good to have something to suggest to them or have more idea what they are talking about.