I had similar issues with a CV64 hanging/freezing during bootup on my A3000. It turned out to be a faulty card, got another one and worked first time. Apparently it is quite a common problem (search the forums here and via search engines) so chances are your card may be to blame.
have you tried the following:
0) Try Picasso 98, an alternative (and for many a better one) to the Cybervision drivers.
1) remove any extra cards / external peripherals and see if it boots then
2) change the resolution to PAL (booting through an alternate startup-sequence) and then to a CV64
3) clean the contacts of the card and the zorro expansion slot. Make sure it makes proper contact.
4) Is your power supply providing enough juice? Use a multimeter to check the 5 and 12 volt lines.
X) if your CV64 is the 4mb model (*only after you've tried all other options*), try physically removing 2mb of memory (I tried this with a tiny screwdriver) from the card and try again.
Good luck and keep us posted on progress!
