OK, I haven't done nothing now and thats gone, but:
A send error report has appeared straight away before I open the game and says "RCT3.exe has to close. We are sorry if this caused any inconveiniences" Yep it has, lol. I click all the options which are: Debug, Do not send Error Report and Send Error report.
I do have DirectX 9.0 installed so thats not it...