When you performed the long test...did your hard drive pass diagnostics? That's the main question...
If it did not, then you need to let us know where the diagnostics failed. You'll either receive a "pass" or "fail" when performing the diagnostics.
As far as, your bootmgr.exe issue...your operating system (Vista) is letting you know that there is a problem with the boot sector...so Vista will not load until you fix the issue. The last link I gave you was to information on how to fix this...and I quote:
Insert your Vista install disk and restart your system. Press any key when prompted to begin running the dvd. Wait for it to give you a list of choices. This may take a while as it often stays a blank screen for some time. Choose "repair", and the setup will auto detect your operating system. It will also fix your bootmgr.exe at this point. If it does not, you can go on to the next screen and choose "startup repair".
Granted...this is done after you configure your computer to boot from your optical drive, which is done in BIOS. All you have to do is boot into BIOS and configure your optical drive to be the first boot device.