Cooker, dave is right.
There is no need to re-install.
Just make sure you take a back up of all your files and database, re-upload your vbulletin folder with all your files.
Then go to phpmyAdmin. Import your database from mySQL (this is fairly simple to do).
After that, all you need to do is like dave said, point your domain to your new nameservers and then simply proceed to go to your old forum url. It will be up and running as if it was always there.
Now, also would like to suggest you give cloudflare a try to protect your website. It's free and some shared host already have it installed. To install it on a vps simply go to the website and point your nameservers to the ones they give you. (you can also install it to your vps using an api key they provide)
If ever you have any DDoS problems or issues of an attack. This will in most cases protect your website from coming offline.
Hope that helped. Have a wonderful day cooker