Bootmgr is missing - Repair says that's all OK

Hi everybody
I've installed Vista RC1 starting from an exterbal dvd (Usb). The
installation was fine (but at opposite of what is written it never restart
during the procedure). Finishing the Expanding file (about 50 minutes) it
goes on to next steps and at the end it restart automatically.
At the reboot on prompt says "BOOTMGR is missin - Press Ctrl-Alt-Del to
reboot)".
So I'vre read many message regarding this trouble and I've tried to use the
repair function from the dvd (it is really boring during the "Windows is
loadin files" phase, about 30 minutes to go).
I've chosen Startup repair , but no problems are found, it seems everything
allright but rebooting the problem is still remain.
So after ia new "Windows is loading files..." phase I've tried to use
Command prompt and with a ScanOS it says this "Total identifies Windows
installations:0". But in Startup Repair it finds th windows Vista on my Hd
"C:".
So I've tried to write a boot.ini manually but it does't works...
So now I've 2 choices
1) Re-try a repair (but I'm skeptic about it)
2) Try a re-installation of o.s.

Any ideas?
Thanks in advance
Ciao
Gianfranco

PS: Could be a problem regarding my dvd that is an external device on usb
port? I don't know because it seems to works during every phases.