Download and burn free Partition Wizard bootable CD
, boot it, select 1 for screen res, rightclick Windows 7, Modify>Set to Active, OK.
Now rightclick Vista to Delete, OK., Apply all steps.
Set Windows 7 as first HD to boot (after DVD) in BIOS setup.
Next boot the Windows 7 DVD Repair console or Repair CD, click through to Recovery Tools list to run Startup Repair up to 3 separate times with reboots to write the MBR to Windows 7.
If Disk Management will still not open, run sfc /scannow as Admin. If this fails, then run a Repair Install