Cubase 6.5 crashing W 7 64 bit

Hi All
Cubase 6.5 has started crashing my dedicated Rain Music PC and Task Manager cannot shut the program down.
This then requires a hard shut-down.
This has happened with different sound-cards , currently M-Audio Ultra.
I’ve tried tech support but am still waiting…
Any help appreciated,
thanks, joe
(a long-time user)