Cubase 7 Crash after 10 min

Hi there…
I’m using Cubase for a long time.
I’ve just upgraded Cubase 7 64bit from 6.5 and I have a HUGE problem,
after 10 min of using Cubase 7 it’s stops no matter what i’m doing! let me explain :
No sound , I can’t exit cubase … I can’t even use the Task Manager, the whole computer is stuck now. :astonished:
The only thing left for me to do is to reboot the computer.
It’s also happens with the 32bit version and with Cubase 6.5 both versions.

I’m using Windows 8 64bit , Q6600 , 8GB - TC electronics Impact Twins.
I’ve never had that proplem before!
PLEASE HELP!!! :cry: I can’t work like this and I’m losing costumers.

Sorry about my english… :confused: