This is not a supported install method. You claim you did this before so what changed?
So I'm installing Windows 7 via a USB, but I'm having troubles to make the USB bootable.
I've installed OS with my USB before; but it doesn't seem to want to make itself bootable.
OS: Ubuntu 12.10
Flash drive: 4GB/HP
Note: I thought it might have been the Windows 7 booter, but I tried to install Ubuntu (64-bit) on the drive and I can say it's the USB.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic