BOOTMGR Problem

I have been running Windows Vista Ultimate x64 on a dual core Athlon
without problems for months. But on booting today I got the dreaded
'BOOTMGR is missing' message during the boot sequence (this was after I
had miistakenly clicked on 'sleep' rather than 'shutdown', which seems
to have damaged something).

I have followed all the options for solving this problem (all three
steps as set out in the Microsoft KB article on the issue) but the
problem reamins stubbornly in place.

But I have discovered by accident that if I leave my x64 Vista disc in
the DVD drive and allow the 'press any key to boot from DVD' prompt to
time out (i.e. without a key press) my system then boots up normally.

I am pretty well resigned to doing a clean reinstall but I thought I
would ask here about the issue in the hope someone might know from the
symptoms what is going wrong and how to fix it.

I would be most grateful for any advice that anyone can offer.

I would hate to spend hours going through a reinstall (and reloading
megabytes of Windows updates) if there is a simple fix.

Brian Gladman