Windows 7 won't boot

Right, whilst I realise there have been many posts on this subject my situation is slightly different. My computer originally came installed with Windows Vista 32-bit and when Widows 7 Ultimate 64-bit was released I wanted to upgrade. Obviously I had to do a custom installation as you can't simply upgrade from a 32-bit to a 64-bit system. To get around this I just installed windows 7 on my other (empty) hard drive. For a while everything worked fine and I had the option to either boot Windows Vista or Windows 7 on startup. I found that I was satisfied with Windows 7 and wanted to get rid of Vista to free up some hard drive space. I used Paragon Partition Manager and Formatted the old Vista drive. I presumed that the system would have no trouble booting Windows 7 as the option had been there when the dual boot was available...how foolish of me. When I restarted the computer text appeared saying "no items to display". Initially I thought that the computer was just trying to boot from the clean harddrive so at the next startup I went into boot options and selected the other drive. I was then informed that "BOOT MGR" was missing and thus it couldn't load. Having misplaced the Windows 7 installation CD I ended up just reinstalling the old Vista OS. Is there any way I can get Windows 7 to boot properly again without doing a full reinstall?

P.S. After going to Computer -> Properties -> Advanced System Settings -> Advanced Tab -> Startup and Recovery Settings and clicking on the Default Operating System drop down menu only Windows Vista was present.

Any help would be greatly appreciated, thanks.

Thanks Ill hunt around for the ever elusive disc.

Thanks SIW2 as I still can't find the damned Windows 7 installation disc this seems like a good option. Will let you know how I get on

As SIW2 advises, set your Win7 HD to be first HD to boot in BIOS, after DVD.

Then boot your Win7 DVD or Repair CD, in Recovery tools open a Command Line to mark the Win7 drive active:

Type:

DISKPART
LIST DISK
SELECT DISK # (for Windows 7 disk)
active
exit

Now return to Recovery tools list and run Startup Repair 3 separate times to rewrite the MBR to Win7.

You may need to unplug the Vista disk to achieve this if it interferes.

Thanks to all your help I'm now typing this from Windows 7, crisis over. The startup repair worked perfectly and I didn't need the install disc. Thanks again for your quick and effective solutions.