Your mention of going through the motions of custom installing ubuntu on a flash drive is all too familiar with what I ran into back in early 2010 when creating data recovery sticks out of larger flash drives custom installing ubuntu or another distro to a second root parttition keeping the first NTFS on them.
The 7 mbr was "trashed" on one install by Grub! I forgot to edition the "mount point /" as the root and see Grub installed to the flash drive instead of the 7 host drive! I ended up running the repair tools booted live from the 7 dvd to rebuild the BCD store which then saw 7 load right again as usual.
For installing any OS I tend to use GParted except when wanting the 100mb System Reserved partition placed on the drive by the Windows installer. The cross platform support makes the live for cd version ideal for setting up any dual boots on the physical drives when not simply seeing a secondary OS go onto a VM.
The ubuntu installer itself has it's own form of GParted and that was why the quesiton had been asked about which partitioning program was used or how you went about deleting partitions. You also referred to the Disk Part tool as well.
The important thing now however since you found the 7 installation and all files are still present rules out C as what you had removed which should be a big relief for you there!
Now the next step is repair of the boot information and files to get you back running again. MBR - Restore Windows 7 Master Boot Record
The Startup repair tool might work on it's own if you run that two or three times restarting inbetween each run. The command prompt would be used for seeing the BCD store rebuilt. Follow the steps closely and you should be back running real soon!