Activated another drive, OOPs!

Ok so story time, was formatting an external harddrive to be able to be read by a PS3 to play some videos. A windows update shuts down the computer formatting it. So its completely blank with no drive letter and cant be picked up by My Computer, so I go and search and find out how to fix this. Disk manager. SO I go there, format but forgot to assign a letter. I right click and accidently assign it as the active drive. Not paying attention I hit yes to the box. I noticed as soon as I did but didnt think it would be a big deal. I could deal with it when I got home. So I go out and later that night come home for some League of Legends. Low and behold BOOTMNGR not found.

But it sees that my main hard drive is in...it just now wont load it correctly I assume. ATM i'm trying to create a bootable copy of my Windows 7 disk on a USB (My new desktop this is on doesnt have a CD tray yet and Microsoft gave me an ISO), but the Windows 7 USB tool isnt recognizing my 14gb USB as one it can use, so I looked online and am now attempting to manually do it via command prompt.

Is there a better solution or am I on the way?