Windows 7 does not natively run Blu-ray
You need a separate software program like "PowerDVD" which contains the stuff you need to run the blu-ray discs.
Were you supplied with the blu-ray software for vista?? - you just have to find out if the company supplies an updated Win 7 version if you bought an upgrade off them.
Otherwise the software costs $100 upwards
Have you checked in 'computer management' for any yellow triangles against the hardware?