Why don´t you go back to Cubase 6.5 for the time being? And your former OS. And check again when 7.02 is ready.
And did you run a memtest program. Going from 4 to 8gb can cause stability issues if not done 100% correctly (qualified ram of same batch/one set and at correct settings) So first thing to try is romove the new 4gb and see if that helps.
The only time I ever had stability issues was when I had flaky ram.