DISKPART> list vol
Volume ### Ltr Label Fs Type Size Status Info
---------- --- ----------- ----- ---------- ------- --------- --------
Volume 0 G DVD-ROM 0 B No Media
Volume 1 H WD SmartWar UDF CD-ROM 668 MB Healthy
* Volume 2 System Rese NTFS Partition 250 MB Healthy System
Volume 3 C Windows 8 P NTFS Partition 352 GB Healthy Boot
Volume 4 F Windows Ser NTFS Partition 244 GB Healthy
Volume 5 D Downloads NTFS Partition 335 GB Healthy
Volume 6 E Storage Spa NTFS Partition 11 TB Healthy
DISKPART>
select volume 2
active
list vol (to confirm that it is now set active)
now that we have an idea of what is going on exit disk part but remember the drive letter that is your operating system:
Put the disk back into the original PC, then boot that PC using the ubcd you burnt, go to the Hard-Disk diagnostics, select the manufacturer's diagnostic of your HD, and then run the long or comprehensive diagnostic. If the tool finds errors which it can't repair, the disk must be replaced. Also run the memtest86+ diagnostic on that CD and if that finds any errors, change out the bad RAM.
If you need to change the disk, you can still connect it as a 2nd disk to your other PC again and copy off any data you shouldn't have a backup of yet.
After changing the disk, just boot from your Original Windows 7 home premium DVD and install the OS from there, or if your old disk is fine and you want to reinstall, do the same. You can delete and create the partitions during the installation. You don't need the Windows 7 Ultimate DVD for that.
To access the registry, you would need to boot into a UBCD4Win (but for that you need a Windows XP CD so you can create the CD). This CD then has several tools which allow you to connect to the registry of the not booted OS and change it's settings:
http://ubcd4win.com