Hi,
after having issues with the aswrvrt.sys before, I installed Avast! again and some months later I still got the same f***ing problem, that forced me to reinstall Windows 7 64 again.
No boot possible, not even in safe mode, reason aswrvrt.sys. Multiboot Vista 32, used uninstall tool, Windows 7 64 almost booted correctly, hung up, same as before.