I had this problem when i first installed W7. Continuous chkdsk after boot and restart, 3-4 times, system starts eventually then after 5 minutes i had information that disk C is corrupted and unreadable (restart, chkdsk and so on).
The only way i could fix this was to install W7 once again, on a new partition formated by installer. After that, new system is running 2nd day and everything seems to be ok. No errors at all so far.
I have also Vista Ult on second partition and it works fine. The only thing i can't understand is that i can't see Vista partition on W7.
Both systems 64-Bit.
Hope that'll work for ya.