Fix my Wordpress host move - possibly DNS related. URGENT!

I have a Wordpress installation that I am moving from one host (Verio) to another host (Bluehost). I have moved the files, database and domain, and switched the DNS but now the emails and wordpress installation are not working. It is clearly 'finding' the new Bluehost hosting because I have set up a simple HTML holding page which it is displaying, but if I go to /wp-admin then it says it cannot connect to the database.

I suspect that this may be related to my DNS settings, or possibly I am just being an idiot and overlooking something simple.

Should be quite a simple fix if you know what you're doing. Unfortunately I have a big deadline for another job and cannot do both at once so hoping somebody here can fix it for me quickly!

Ideally would like fixed tonight if possible.