can a trusted member be banned in a forum of minute

Well they do own the forum so technically they can do that.. It's up to the owner's of whichever forum they will. Usually to get your account back the only way is to work something out with the website admins since they are the ones who have the power to ban/unban people. Read their forums rules to see if you actually broke them. You may be able to dispute their reason for banning you if you have some legitimate points against them. It's worth a try anyway, worst that can happen is they don't give you your account back.

Why don't you contact the Admin of the forum and ask why you were banned? Read the Terms and Rules carefully before you do. I am sure that it says that they are perfectly entitled to ban you for any (or no) reason.

For whatever reason they've banned you and banning tends to be permanent no matter what the forum is. I don't know if you can get your account back because it depends on whether or not they IP banned you. If they've done that, then you won't even be able to view the forum and you will have no hope at all. If you can still view the forums, you may still be able to contact the administrator of it and ask them to review the ban, putting forward your side of the discussion. At the end of the day though, it depends on who the administrator is, what mood they're in and why they banned you in the first place. Sorry if that isn't much help.